- 29 Dec, 2023 23 commits
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Stefan Roesch authored
This adds four new knobs for the KSM advisor to influence its behaviour. The knobs are: - advisor_mode: none: no advisor (default) scan-time: scan time advisor - advisor_max_cpu: 70 (default, cpu usage percent) - advisor_min_pages_to_scan: 500 (default) - advisor_max_pages_to_scan: 30000 (default) - advisor_target_scan_time: 200 (default in seconds) The new values will take effect on the next scan round. Link: https://lkml.kernel.org/r/20231218231054.1625219-3-shr@devkernel.ioSigned-off-by:Stefan Roesch <shr@devkernel.io> Acked-by:
David Hildenbrand <david@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@surriel.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org>
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Stefan Roesch authored
Patch series "mm/ksm: Add ksm advisor", v5. What is the KSM advisor? ========================= The ksm advisor automatically manages the pages_to_scan setting to achieve a target scan time. The target scan time defines how many seconds it should take to scan all the candidate KSM pages. In other words the pages_to_scan rate is changed by the advisor to achieve the target scan time. Why do we need a KSM advisor? ============================== The number of candidate pages for KSM is dynamic. It can often be observed that during the startup of an application more candidate pages need to be processed. Without an advisor the pages_to_scan parameter needs to be sized for the maximum number of candidate pages. With the scan time advisor the pages_to_scan parameter based can be changed based on demand. Algorithm ========== The algorithm calculates the change value based on the target scan time and the previous scan time. To avoid pertubations an exponentially weighted moving average is applied. The algorithm has a max and min value to: - guarantee responsiveness to changes - to limit CPU resource consumption Parameters to influence the KSM scan advisor ============================================= The respective parameters are: - ksm_advisor_mode 0: None (default), 1: scan time advisor - ksm_advisor_target_scan_time how many seconds a scan should of all candidate pages take - ksm_advisor_max_cpu upper limit for the cpu usage in percent of the ksmd background thread The initial value and the max value for the pages_to_scan parameter can be limited with: - ksm_advisor_min_pages_to_scan minimum value for pages_to_scan per batch - ksm_advisor_max_pages_to_scan maximum value for pages_to_scan per batch The default settings for the above two parameters should be suitable for most workloads. The parameters are exposed as knobs in /sys/kernel/mm/ksm. By default the scan time advisor is disabled. Currently there are two advisors: - none and - scan-time. Resource savings ================= Tests with various workloads have shown considerable CPU savings. Most of the workloads I have investigated have more candidate pages during startup. Once the workload is stable in terms of memory, the number of candidate pages is reduced. Without the advisor, the pages_to_scan needs to be sized for the maximum number of candidate pages. So having this advisor definitely helps in reducing CPU consumption. For the instagram workload, the advisor achieves a 25% CPU reduction. Once the memory is stable, the pages_to_scan parameter gets reduced to about 40% of its max value. The new advisor works especially well if the smart scan feature is also enabled. How is defining a target scan time better? =========================================== For an administrator it is more logical to set a target scan time.. The administrator can determine how many pages are scanned on each scan. Therefore setting a target scan time makes more sense. In addition the administrator might have a good idea about the memory sizing of its respective workloads. Setting cpu limits is easier than setting The pages_to_scan parameter. The pages_to_scan parameter is per batch. For the administrator it is difficult to set the pages_to_scan parameter. Tracing ======= A new tracing event has been added for the scan time advisor. The new trace event is called ksm_advisor. It reports the scan time, the new pages_to_scan setting and the cpu usage of the ksmd background thread. Other approaches ================= Approach 1: Adapt pages_to_scan after processing each batch. If KSM merges pages, increase the scan rate, if less KSM pages, reduce the the pages_to_scan rate. This doesn't work too well. While it increases the pages_to_scan for a short period, but generally it ends up with a too low pages_to_scan rate. Approach 2: Adapt pages_to_scan after each scan. The problem with that approach is that the calculated scan rate tends to be high. The more aggressive KSM scans, the more pages it can de-duplicate. There have been earlier attempts at an advisor: propose auto-run mode of ksm and its tests (https://marc.info/?l=linux-mm&m=166029880214485&w=2) This patch (of 5): This adds the ksm advisor. The ksm advisor automatically manages the pages_to_scan setting to achieve a target scan time. The target scan time defines how many seconds it should take to scan all the candidate KSM pages. In other words the pages_to_scan rate is changed by the advisor to achieve the target scan time. The algorithm has a max and min value to: - guarantee responsiveness to changes - limit CPU resource consumption The respective parameters are: - ksm_advisor_target_scan_time (how many seconds a scan should take) - ksm_advisor_max_cpu (maximum value for cpu percent usage) - ksm_advisor_min_pages (minimum value for pages_to_scan per batch) - ksm_advisor_max_pages (maximum value for pages_to_scan per batch) The algorithm calculates the change value based on the target scan time and the previous scan time. To avoid pertubations an exponentially weighted moving average is applied. The advisor is managed by two main parameters: target scan time, cpu max time for the ksmd background thread. These parameters determine how aggresive ksmd scans. In addition there are min and max values for the pages_to_scan parameter to make sure that its initial and max values are not set too low or too high. This ensures that it is able to react to changes quickly enough. The default values are: - target scan time: 200 secs - max cpu: 70% - min pages: 500 - max pages: 30000 By default the advisor is disabled. Currently there are two advisors: none and scan-time. Tests with various workloads have shown considerable CPU savings. Most of the workloads I have investigated have more candidate pages during startup, once the workload is stable in terms of memory, the number of candidate pages is reduced. Without the advisor, the pages_to_scan needs to be sized for the maximum number of candidate pages. So having this advisor definitely helps in reducing CPU consumption. For the instagram workload, the advisor achieves a 25% CPU reduction. Once the memory is stable, the pages_to_scan parameter gets reduced to about 40% of its max value. Link: https://lkml.kernel.org/r/20231218231054.1625219-1-shr@devkernel.io Link: https://lkml.kernel.org/r/20231218231054.1625219-2-shr@devkernel.ioSigned-off-by:
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Matthew Wilcox (Oracle) authored
All callers have now been converted to folio_add_new_anon_rmap() and folio_add_lru_vma() so we can remove the wrapper. Link: https://lkml.kernel.org/r/20231211162214.2146080-10-willy@infradead.orgSigned-off-by:
Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by:
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Matthew Wilcox (Oracle) authored
Replace three calls to compound_head() with one. Link: https://lkml.kernel.org/r/20231211162214.2146080-9-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
Replaces five calls to compound_head() with one. Link: https://lkml.kernel.org/r/20231211162214.2146080-8-willy@infradead.orgSigned-off-by:
Alistair Popple <apopple@nvidia.com> Signed-off-by:
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Matthew Wilcox (Oracle) authored
Refer to folio_add_new_anon_rmap() instead. Link: https://lkml.kernel.org/r/20231211162214.2146080-7-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
folio_add_new_anon_rmap() no longer works this way, so just remove the entire example. Link: https://lkml.kernel.org/r/20231211162214.2146080-6-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
We already have the folio in these functions, we just need to use it. folio_add_new_anon_rmap() didn't exist at the time they were converted to folios. Link: https://lkml.kernel.org/r/20231211162214.2146080-5-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
Saves about eight calls to compound_head(). Link: https://lkml.kernel.org/r/20231211162214.2146080-4-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
The page in question is either freshly allocated or known to be in the swap cache; these assertions are not particularly useful. Link: https://lkml.kernel.org/r/20231212164813.2540119-1-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
Patch series "Finish two folio conversions". Most callers of page_add_new_anon_rmap() and lru_cache_add_inactive_or_unevictable() have been converted to their folio equivalents, but there are still a few stragglers. There's a bit of preparatory work in ksm and unuse_pte(), but after that it's pretty mechanical. This patch (of 9): Accept a folio as an argument and return a folio result. Removes a call to compound_head() in do_swap_page(), and prevents folio & page from getting out of sync in unuse_pte(). Reviewed-by:
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Suren Baghdasaryan authored
Add tests for new UFFDIO_MOVE ioctl which uses uffd to move source into destination buffer while checking the contents of both after the move. After the operation the content of the destination buffer should match the original source buffer's content while the source buffer should be zeroed. Separate tests are designed for PMD aligned and unaligned cases because they utilize different code paths in the kernel. Link: https://lkml.kernel.org/r/20231206103702.3873743-6-surenb@google.comSigned-off-by:
Suren Baghdasaryan <surenb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by:
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Suren Baghdasaryan authored
Currently each test can specify unique operations using uffd_test_ops, however these operations are per-memory type and not per-test. Add uffd_test_case_ops which each test case can customize for its own needs regardless of the memory type being used. Pre- and post-allocation operations are added, some of which will be used in the next patch to implement test-specific operations like madvise after memory is allocated but before it is accessed. Link: https://lkml.kernel.org/r/20231206103702.3873743-5-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
uffd_test_ctx_clear() is being called from uffd_test_ctx_init() to unmap areas used in the previous test run. This approach is problematic because while unmapping areas uffd_test_ctx_clear() uses page_size and nr_pages which might differ from one test run to another. Fix this by calling uffd_test_ctx_clear() after each test is done. Link: https://lkml.kernel.org/r/20231206103702.3873743-4-surenb@google.comSigned-off-by:
Peter Xu <peterx@redhat.com> Reviewed-by:
Axel Rasmussen <axelrasmussen@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by:
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Andrea Arcangeli authored
Implement the uABI of UFFDIO_MOVE ioctl. UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application needs pages to be allocated [1]. However, with UFFDIO_MOVE, if pages are available (in userspace) for recycling, as is usually the case in heap compaction algorithms, then we can avoid the page allocation and memcpy (done by UFFDIO_COPY). Also, since the pages are recycled in the userspace, we avoid the need to release (via madvise) the pages back to the kernel [2]. We see over 40% reduction (on a Google pixel 6 device) in the compacting thread's completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was measured using a benchmark that emulates a heap compaction implementation using userfaultfd (to allow concurrent accesses by application threads). More details of the usecase are explained in [2]. Furthermore, UFFDIO_MOVE enables moving swapped-out pages without touching them within the same vma. Today, it can only be done by mremap, however it forces splitting the vma. [1] https://lore.kernel.org/all/1425575884-2574-1-git-send-email-aarcange@redhat.com/ [2] https://lore.kernel.org/linux-mm/CA+EESO4uO84SSnBhArH4HvLNhaUQ5nZKNKXqxRCyjniNVjp0Aw@mail.gmail.com/ Update for the ioctl_userfaultfd(2) manpage: UFFDIO_MOVE (Since Linux xxx) Move a continuous memory chunk into the userfault registered range and optionally wake up the blocked thread. The source and destination addresses and the number of bytes to move are specified by the src, dst, and len fields of the uffdio_move structure pointed to by argp: struct uffdio_move { __u64 dst; /* Destination of move */ __u64 src; /* Source of move */ __u64 len; /* Number of bytes to move */ __u64 mode; /* Flags controlling behavior of move */ __s64 move; /* Number of bytes moved, or negated error */ }; The following value may be bitwise ORed in mode to change the behavior of the UFFDIO_MOVE operation: UFFDIO_MOVE_MODE_DONTWAKE Do not wake up the thread that waits for page-fault resolution UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES Allow holes in the source virtual range that is being moved. When not specified, the holes will result in ENOENT error. When specified, the holes will be accounted as successfully moved memory. This is mostly useful to move hugepage aligned virtual regions without knowing if there are transparent hugepages in the regions or not, but preventing the risk of having to split the hugepage during the operation. The move field is used by the kernel to return the number of bytes that was actually moved, or an error (a negated errno- style value). If the value returned in move doesn't match the value that was specified in len, the operation fails with the error EAGAIN. The move field is output-only; it is not read by the UFFDIO_MOVE operation. The operation may fail for various reasons. Usually, remapping of pages that are not exclusive to the given process fail; once KSM might deduplicate pages or fork() COW-shares pages during fork() with child processes, they are no longer exclusive. Further, the kernel might only perform lightweight checks for detecting whether the pages are exclusive, and return -EBUSY in case that check fails. To make the operation more likely to succeed, KSM should be disabled, fork() should be avoided or MADV_DONTFORK should be configured for the source VMA before fork(). This ioctl(2) operation returns 0 on success. In this case, the entire area was moved. On error, -1 is returned and errno is set to indicate the error. Possible errors include: EAGAIN The number of bytes moved (i.e., the value returned in the move field) does not equal the value that was specified in the len field. EINVAL Either dst or len was not a multiple of the system page size, or the range specified by src and len or dst and len was invalid. EINVAL An invalid bit was specified in the mode field. ENOENT The source virtual memory range has unmapped holes and UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set. EEXIST The destination virtual memory range is fully or partially mapped. EBUSY The pages in the source virtual memory range are either pinned or not exclusive to the process. The kernel might only perform lightweight checks for detecting whether the pages are exclusive. To make the operation more likely to succeed, KSM should be disabled, fork() should be avoided or MADV_DONTFORK should be configured for the source virtual memory area before fork(). ENOMEM Allocating memory needed for the operation failed. ESRCH The target process has exited at the time of a UFFDIO_MOVE operation. Link: https://lkml.kernel.org/r/20231206103702.3873743-3-surenb@google.comSigned-off-by:
Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:
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Andrea Arcangeli authored
Patch series "userfaultfd move option", v6. This patch series introduces UFFDIO_MOVE feature to userfaultfd, which has long been implemented and maintained by Andrea in his local tree [1], but was not upstreamed due to lack of use cases where this approach would be better than allocating a new page and copying the contents. Previous upstraming attempts could be found at [6] and [7]. UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application needs pages to be allocated [2]. However, with UFFDIO_MOVE, if pages are available (in userspace) for recycling, as is usually the case in heap compaction algorithms, then we can avoid the page allocation and memcpy (done by UFFDIO_COPY). Also, since the pages are recycled in the userspace, we avoid the need to release (via madvise) the pages back to the kernel [3]. We see over 40% reduction (on a Google pixel 6 device) in the compacting thread's completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was measured using a benchmark that emulates a heap compaction implementation using userfaultfd (to allow concurrent accesses by application threads). More details of the usecase are explained in [3]. Furthermore, UFFDIO_MOVE enables moving swapped-out pages without touching them within the same vma. Today, it can only be done by mremap, however it forces splitting the vma. TODOs for follow-up improvements: - cross-mm support. Known differences from single-mm and missing pieces: - memcg recharging (might need to isolate pages in the process) - mm counters - cross-mm deposit table moves - cross-mm test - document the address space where src and dest reside in struct uffdio_move - TLB flush batching. Will require extensive changes to PTL locking in move_pages_pte(). OTOH that might let us reuse parts of mremap code. This patch (of 5): For now, folio_move_anon_rmap() was only used to move a folio to a different anon_vma after fork(), whereby the root anon_vma stayed unchanged. For that, it was sufficient to hold the folio lock when calling folio_move_anon_rmap(). However, we want to make use of folio_move_anon_rmap() to move folios between VMAs that have a different root anon_vma. As folio_referenced() performs an RMAP walk without holding the folio lock but only holding the anon_vma in read mode, holding the folio lock is insufficient. When moving to an anon_vma with a different root anon_vma, we'll have to hold both, the folio lock and the anon_vma lock in write mode. Consequently, whenever we succeeded in folio_lock_anon_vma_read() to read-lock the anon_vma, we have to re-check if the mapping was changed in the meantime. If that was the case, we have to retry. Note that folio_move_anon_rmap() must only be called if the anon page is exclusive to a process, and must not be called on KSM folios. This is a preparation for UFFDIO_MOVE, which will hold the folio lock, the anon_vma lock in write mode, and the mmap_lock in read mode. Link: https://lkml.kernel.org/r/20231206103702.3873743-1-surenb@google.com Link: https://lkml.kernel.org/r/20231206103702.3873743-2-surenb@google.comSigned-off-by:
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Matthew Wilcox (Oracle) authored
Both __block_write_full_folio() and block_read_full_folio() assumed that block size <= PAGE_SIZE. Replace the shift with a divide, which is probably cheaper than first calculating the shift. That lets us remove block_size_bits() as these were the last callers. Link: https://lkml.kernel.org/r/20231109210608.2252323-8-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
When __block_write_begin_int() was converted to support folios, we did not expect large folios to be passed to it. With the current work to support large block size storage devices, this will no longer be true so change the checks on 'from' and 'to' to be related to the size of the folio instead of PAGE_SIZE. Also remove an assumption that the block size is smaller than PAGE_SIZE. Link: https://lkml.kernel.org/r/20231109210608.2252323-7-willy@infradead.orgSigned-off-by:
Ryusuke Konishi <konishi.ryusuke@gmail.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Pankaj Raghav <p.raghav@samsung.com> Signed-off-by:
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Matthew Wilcox (Oracle) authored
If i_blkbits is larger than PAGE_SHIFT, we shift by a negative number, which is undefined. It is safe to shift the block left as a block device must be smaller than MAX_LFS_FILESIZE, which is guaranteed to fit in loff_t. Link: https://lkml.kernel.org/r/20231109210608.2252323-6-willy@infradead.orgSigned-off-by:
Pankaj Raghav <p.raghav@samsung.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by:
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Matthew Wilcox (Oracle) authored
While sector_t is always defined as a u64 today, that hasn't always been the case and it might not always be the same size as loff_t in the future. Link: https://lkml.kernel.org/r/20231109210608.2252323-5-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
We must not shift by a negative number so work in terms of a byte offset to avoid the awkward shift left-or-right-depending-on-sign option. This means we need to use check_mul_overflow() to ensure that a large block number does not result in a wrap. Link: https://lkml.kernel.org/r/20231109210608.2252323-4-willy@infradead.orgSigned-off-by:
Nathan Chancellor <nathan@kernel.org> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Pankaj Raghav <p.raghav@samsung.com> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> [nathan@kernel.org: add cast in grow_buffers() to avoid a multiplication libcall] Link: https://lkml.kernel.org/r/20231128-avoid-muloti4-grow_buffers-v1-1-bc3d0f0ec483@kernel.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
The calculation of block from index doesn't work for devices with a block size larger than PAGE_SIZE as we end up shifting by a negative number. Instead, calculate the number of the first block from the folio's position in the block device. We no longer need to pass sizebits to grow_dev_folio(). Link: https://lkml.kernel.org/r/20231109210608.2252323-3-willy@infradead.orgSigned-off-by:
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Matthew Wilcox (Oracle) authored
Patch series "More buffer_head cleanups", v2. The first patch is a left-over from last cycle. The rest fix "obvious" block size > PAGE_SIZE problems. I haven't tested with a large block size setup (but I have done an ext4 xfstests run). This patch (of 7): Rename grow_dev_page() to grow_dev_folio() and make it return a bool. Document what that bool means; it's more subtle than it first appears. Also rename the 'failed' label to 'unlock' beacuse it's not exactly 'failed'. It just hasn't succeeded. Link: https://lkml.kernel.org/r/20231109210608.2252323-2-willy@infradead.orgSigned-off-by:
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- 20 Dec, 2023 17 commits
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Borislav Petkov (AMD) authored
Use the same splat markers as panic does for easier matching by external tools scanning kernel dmesg for splats. Link: https://lkml.kernel.org/r/20231218135339.23209-1-bp@alien8.deSigned-off-by:
Borislav Petkov (AMD) <bp@alien8.de> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Signed-off-by:
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Yajun Deng authored
There is redundant code in __free_pages_ok(). Use free_one_page() simplify it. Link: https://lkml.kernel.org/r/20231216030503.2126130-1-yajun.deng@linux.devSigned-off-by:
Yajun Deng <yajun.deng@linux.dev> Reviewed-by:
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Peng Zhang authored
The last range stored in maple tree is typically quite large. By checking if it exceeds the sum of the remaining ranges in that node, it is possible to avoid checking all other gaps. Running the maple tree test suite in user mode almost always results in a near 100% hit rate for this optimization. Link: https://lkml.kernel.org/r/20231215074632.82045-1-zhangpeng.00@bytedance.comSigned-off-by:
Peng Zhang <zhangpeng.00@bytedance.com> Reviewed-by:
Liam R. Howlett <Liam.Howlett@oracle.com> Signed-off-by:
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Fabio M. De Francesco authored
kmap() has been deprecated in favor of kmap_local_page(). Therefore, replace kmap() with kmap_local_page() in mm/memory.c. There are two main problems with kmap(): (1) It comes with an overhead as the mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap's pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page-faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. The tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and still valid. Obviously, thread locality implies that the kernel virtual addresses returned by kmap_local_page() are only valid in the context of the callers (i.e., they cannot be handed to other threads). The use of kmap_local_page() in mm/memory.c does not break the above-mentioned assumption, so it is allowed and preferred. Link: https://lkml.kernel.org/r/20231215084417.2002370-1-fabio.maria.de.francesco@linux.intel.com Link: https://lkml.kernel.org/r/20231214081039.1919328-1-fabio.maria.de.francesco@linux.intel.comSigned-off-by:
Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com> Reviewed-by:
Ira Weiny <ira.weiny@intel.com> Signed-off-by:
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Randy Dunlap authored
Correct typos/spellos and punctutation. Link: https://lkml.kernel.org/r/20231213043316.10128-1-rdunlap@infradead.orgSigned-off-by:
Randy Dunlap <rdunlap@infradead.org> Signed-off-by:
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SeongJae Park authored
There are eight command inputs for 'state' DAMON sysfs file, and those are verbosely explained in multiple paragraphs. It is not easy to find explanation of specific command, and getting whole picture of supported commands. Replace the paragraphs with a list. Link: https://lkml.kernel.org/r/20231213190338.54146-7-sj@kernel.orgSigned-off-by:
SeongJae Park <sj@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by:
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SeongJae Park authored
'Sysfs Files Hierarchy' section of DAMON usage document shows whole picture of the interface. Then sections for detailed explanation of the files follow. Due to the amount of the files, navigating between the whole picture and the section for specific files sometimes require no subtle amount of scrolling. Add links from the whole picture to the dedicated sections for making the navigation easier. Link: https://lkml.kernel.org/r/20231213190338.54146-6-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
The label for context DAMON sysfs directory section is having name sysfs_contexts. The name would be better to be used for the contexts directory. Rename it to represent a single context. Link: https://lkml.kernel.org/r/20231213190338.54146-5-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
The execution model and data structures section at the end of the design document is briefly explaining how DAMON works overall. Knowing that first may help better drawing the overall picture. It may also help better understanding following detailed sections. Move it to the beginning of the document. Link: https://lkml.kernel.org/r/20231213190338.54146-4-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
Commit 35f5d941 ("mm/damon: implement a function for max nr_accesses safe calculation") has fixed an overflow bug that could cause divide-by-zero. Add a kunit test for the bug to ensure similar bugs are not introduced again. Link: https://lkml.kernel.org/r/20231213190338.54146-3-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
Patch series "mm/damon: misc updates for 6.8". Update comments, tests, and documents for DAMON. This patch (of 6): SeongJae is using his kernel.org account for DAMON development. Update the old email addresses on the comments of DAMON source files. Link: https://lkml.kernel.org/r/20231213190338.54146-1-sj@kernel.org Link: https://lkml.kernel.org/r/20231213190338.54146-2-sj@kernel.orgSigned-off-by:
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Kevin Hao authored
A freezable kernel thread can enter frozen state during freezing by either calling try_to_freeze() or using wait_event_freezable() and its variants. However, there is no need to use both methods simultaneously. Link: https://lkml.kernel.org/r/20231213090906.1070985-1-haokexin@gmail.comSigned-off-by:
Kevin Hao <haokexin@gmail.com> Acked-by:
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SeongJae Park authored
Add a test for reproducing the update_schemes_tried_{regions,bytes} command-causing indefinite hang bug that fixed by commit 7d6fa31a ("mm/damon/sysfs-schemes: add timeout for update_schemes_tried_regions"), to avoid mistakenly re-introducing the bug. Refer to the fix commit for more details of the bug. Link: https://lkml.kernel.org/r/20231212194810.54457-6-sj@kernel.orgSigned-off-by: -
SeongJae Park authored
Add a selftest for verifying the accuracy of DAMON's access monitoring functionality. The test starts a program of artificial access pattern, monitor the access pattern using DAMON, and check if DAMON finds expected amount of hot data region (working set size) with only acceptable error rate. Note that the acceptable error rate is set with only naive assumptions and small number of tests. Hence failures of the test may not always mean DAMON is broken. Rather than that, those could be a signal to better understand the real accuracy level of DAMON in wider environments. Based on further finding, we could optimize DAMON or adjust the expectation of the test. Link: https://lkml.kernel.org/r/20231212194810.54457-5-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
Implement update_schemes_tried_bytes command of DAMON sysfs interface in _damon_sysfs.py. It is not only making the update, but also read the updated value from the sysfs interface and store it in the Kdamond python objects so that the user of the module can easily get the value. Link: https://lkml.kernel.org/r/20231212194810.54457-4-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
Extend the tests-writing-purpose DAMON sysfs control module to support the kdamonds start functionality. Link: https://lkml.kernel.org/r/20231212194810.54457-3-sj@kernel.orgSigned-off-by:
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SeongJae Park authored
Patch series "selftests/damon: add Python-written DAMON functionality tests", v2. DAMON exports most of its functionality via its sysfs interface. Hence most DAMON functionality tests could be implemented using the interface. However, because the interfaces require simple but multiple operations for many controls, writing all such tests from the scratch could be repetitive and time consuming. Implement a minimum DAMON sysfs control module, and a couple of DAMON functionality tests using the control module. The first test is for ensuring minimum accuracy of data access monitoring, and the second test is for finding if a previously found and fixed bug is introduced again. Note that the DAMON sysfs control module is only for avoiding duplicating code in tests. For convenient and general control of DAMON, users should use DAMON user-space tools that developed for the purpose, such as damo[1]. [1] https://github.com/damonitor/damo Patches Sequence ---------------- This patchset is constructed with five patches. The first three patches implement a Python-written test implementation-purpose DAMON sysfs control module. The implementation is incrementally done in the sequence of the basic data structure (first patch) first, kdamonds start command (second patch) next, and finally DAMOS tried bytes update command (third patch). Then two patches for implementing selftests using the module follows. The fourth patch implements a basic functionality test of DAMON for working set estimation accuracy. Finally, the fifth patch implements a corner case test for a previously found bug. This patch (of 5): Implement a python module for DAMON sysfs controls. The module is aimed to be useful for writing DAMON functionality tests in future. Nonetheless, this module is only representing a subset of DAMON sysfs files. Following commits will implement more DAMON sysfs controls. Link: https://lkml.kernel.org/r/20231212194810.54457-1-sj@kernel.org Link: https://lkml.kernel.org/r/20231212194810.54457-2-sj@kernel.orgSigned-off-by:
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