- 22 Sep, 2009 40 commits
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Mel Gorman authored
Fragmentation avoidance depends on being able to use free pages from lists of the appropriate migrate type. In the event this is not possible, __rmqueue_fallback() selects a different list and in some circumstances change the migratetype of the pageblock. Simplistically, the more times this event occurs, the more likely that fragmentation will be a problem later for hugepage allocation at least but there are other considerations such as the order of page being split to satisfy the allocation. This patch adds a trace event for __rmqueue_fallback() that reports what page is being used for the fallback, the orders of relevant pages, the desired migratetype and the migratetype of the lists being used, whether the pageblock changed type and whether this event is important with respect to fragmentation avoidance or not. This information can be used to help analyse fragmentation avoidance and help decide whether min_free_kbytes should be increased or not. Signed-off-by:
Mel Gorman <mel@csn.ul.ie> Acked-by:
Rik van Riel <riel@redhat.com> Reviewed-by:
Ingo Molnar <mingo@elte.hu> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Li Ming Chun <macli@brc.ubc.ca> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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Mel Gorman authored
This patch adds trace events for the allocation and freeing of pages, including the freeing of pagevecs. Using the events, it will be known what struct page and pfns are being allocated and freed and what the call site was in many cases. The page alloc tracepoints be used as an indicator as to whether the workload was heavily dependant on the page allocator or not. You can make a guess based on vmstat but you can't get a per-process breakdown. Depending on the call path, the call_site for page allocation may be __get_free_pages() instead of a useful callsite. Instead of passing down a return address similar to slab debugging, the user should enable the stacktrace and seg-addr options to get a proper stack trace. The pagevec free tracepoint has a different usecase. It can be used to get a idea of how many pages are being dumped off the LRU and whether it is kswapd doing the work or a process doing direct reclaim. Signed-off-by:
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by:
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Mel Gorman authored
The function free_cold_page() has no callers so delete it. Signed-off-by:
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Geert Uytterhoeven authored
Commit 96177299 ("Drop free_pages()") modified nr_free_pages() to return 'unsigned long' instead of 'unsigned int'. This made the casts to 'unsigned long' in most callers superfluous, so remove them. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by:
Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com> Reviewed-by:
Christoph Lameter <cl@linux-foundation.org> Acked-by:
Russell King <rmk+kernel@arm.linux.org.uk> Acked-by:
David S. Miller <davem@davemloft.net> Acked-by:
Kyle McMartin <kyle@mcmartin.ca> Acked-by:
WANG Cong <xiyou.wangcong@gmail.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Haavard Skinnemoen <hskinnemoen@atmel.com> Cc: Mikael Starvik <starvik@axis.com> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Hirokazu Takata <takata@linux-m32r.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: David Howells <dhowells@redhat.com> Acked-by:
Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Chris Zankel <zankel@tensilica.com> Cc: Michal Simek <monstr@monstr.eu> Signed-off-by:
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KAMEZAWA Hiroyuki authored
/proc/kcore has its own routine to access vmallc area. It can be replaced with vread(). And by this, /proc/kcore can do safe access to vmalloc area. Signed-off-by:
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: WANG Cong <xiyou.wangcong@gmail.com> Cc: Mike Smith <scgtrp@gmail.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by:
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KAMEZAWA Hiroyuki authored
vread/vwrite access vmalloc area without checking there is a page or not. In most case, this works well. In old ages, the caller of get_vm_ara() is only IOREMAP and there is no memory hole within vm_struct's [addr...addr + size - PAGE_SIZE] ( -PAGE_SIZE is for a guard page.) After per-cpu-alloc patch, it uses get_vm_area() for reserve continuous virtual address but remap _later_. There tend to be a hole in valid vmalloc area in vm_struct lists. Then, skip the hole (not mapped page) is necessary. This patch updates vread/vwrite() for avoiding memory hole. Routines which access vmalloc area without knowing for which addr is used are - /proc/kcore - /dev/kmem kcore checks IOREMAP, /dev/kmem doesn't. After this patch, IOREMAP is checked and /dev/kmem will avoid to read/write it. Fixes to /proc/kcore will be in the next patch in series. Signed-off-by:
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KAMEZAWA Hiroyuki authored
vmap area should be purged after vm_struct is removed from the list because vread/vwrite etc...believes the range is valid while it's on vm_struct list. Signed-off-by:
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Mel Gorman authored
page-allocator: change migratetype for all pageblocks within a high-order page during __rmqueue_fallback When there are no pages of a target migratetype free, the page allocator selects a high-order block of another migratetype to allocate from. When the order of the page taken is greater than pageblock_order, all pageblocks within that high-order page should change migratetype so that pages are later freed to the correct free-lists. The current behaviour is that pageblocks change migratetype if the order being split matches the pageblock_order. When pageblock_order < MAX_ORDER-1, ownership is not changing correct and pages are being later freed to the incorrect list and this impacts fragmentation avoidance. This patch changes all pageblocks within the high-order page being split to the correct migratetype. Without the patch, allocation success rates for hugepages under stress were about 59% of physical memory on x86-64. With the patch applied, this goes up to 65%. Signed-off-by:
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Benjamin Herrenschmidt authored
Right now, if you inadvertently pass NULL to kmem_cache_create() at boot time, it crashes much later after boot somewhere deep inside sysfs which makes it very non obvious to figure out what's going on. Signed-off-by:
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Moussa A. Ba authored
The patch makes the clear_refs more versatile in adding the option to select anonymous pages or file backed pages for clearing. This addition has a measurable impact on user space application performance as it decreases the number of pagewalks in scenarios where one is only interested in a specific type of page (anonymous or file mapped). The patch adds anonymous and file backed filters to the clear_refs interface. echo 1 > /proc/PID/clear_refs resets the bits on all pages echo 2 > /proc/PID/clear_refs resets the bits on anonymous pages only echo 3 > /proc/PID/clear_refs resets the bits on file backed pages only Any other value is ignored Signed-off-by:
Moussa A. Ba <moussa.a.ba@gmail.com> Signed-off-by:
Jared E. Hulbert <jaredeh@gmail.com> Acked-by:
David Rientjes <rientjes@google.com> Signed-off-by:
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Hugh Dickins authored
mremap move's use of ksm_madvise() was assuming -ENOMEM on failure, because ksm_madvise used to say -EAGAIN for that; but ksm_madvise now says -ENOMEM (letting madvise convert that to -EAGAIN), and can also say -ERESTARTSYS when signalled: so pass the error from ksm_madvise. Signed-off-by:
Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by:
Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:
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Hugh Dickins authored
Just as the swapoff system call allocates many pages of RAM to various processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run" (unmerge) is liable to allocate many pages of RAM to various processes, perhaps triggering OOM; and each is normally run from a modest admin process (swapoff or shell), easily repeated until it succeeds. So treat unmerge_and_remove_all_rmap_items() in the same way that we treat try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and bracket both with that, to ask the OOM killer to kill them first, to prevent them from spawning more and more OOM kills. Signed-off-by:
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Hugh Dickins authored
A few cleanups, given the munlock fix: the comment on ksm_test_exit() no longer applies, and it can be made private to ksm.c; there's no more reference to mmu_gather or tlb.h, and mmap.c doesn't need ksm.h. Signed-off-by:
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Hugh Dickins authored
KSM originally stood for Kernel Shared Memory: but the kernel has long supported shared memory, and VM_SHARED and VM_MAYSHARE vmas, and KSM is something else. So we switched to saying "merge" instead of "share". But Chris Wright points out that this is confusing where mmap.c merges adjacent vmas: most especially in the name VM_MERGEABLE_FLAGS, used by is_mergeable_vma() to let vmas be merged despite flags being different. Call it VMA_MERGE_DESPITE_FLAGS? Perhaps, but at present it consists only of VM_CAN_NONLINEAR: so for now it's clearer on all sides to use that directly, with a comment on it in is_mergeable_vma(). Signed-off-by:
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Hugh Dickins authored
Add Documentation/vm/ksm.txt: how to use the Kernel Samepage Merging feature Signed-off-by:
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Hugh Dickins authored
At present KSM is just a waste of space if you don't have CONFIG_SYSFS=y to provide the /sys/kernel/mm/ksm files to tune and activate it. Make KSM depend on SYSFS? Could do, but it might be better to provide some defaults so that KSM works out-of-the-box, ready for testers to madvise MADV_MERGEABLE, even without SYSFS. Though anyone serious is likely to want to retune the numbers to their taste once they have experience; and whether these settings ever reach 2.6.32 can be discussed along the way. Save 1kB from tiny kernels by #ifdef'ing the SYSFS side of it. Signed-off-by:
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Andrea Arcangeli authored
Rawhide users have reported hang at startup when cryptsetup is run: the same problem can be simply reproduced by running a program int main() { mlockall(MCL_CURRENT | MCL_FUTURE); return 0; } The problem is that exit_mmap() applies munlock_vma_pages_all() to clean up VM_LOCKED areas, and its current implementation (stupidly) tries to fault in absent pages, for example where PROT_NONE prevented them being faulted in when mlocking. Whereas the "ksm: fix oom deadlock" patch, knowing there's a race by which KSM might try to fault in pages after exit_mmap() had finally zapped the range, backs out of such faults doing nothing when its ksm_test_exit() notices mm_users 0. So revert that part of "ksm: fix oom deadlock" which moved the ksm_exit() call from before exit_mmap() to the middle of exit_mmap(); and remove those ksm_test_exit() checks from the page fault paths, so allowing the munlocking to proceed without interference. ksm_exit, if there are rmap_items still chained on this mm slot, takes mmap_sem write side: so preventing KSM from working on an mm while exit_mmap runs. And KSM will bail out as soon as it notices that mm_users is already zero, thanks to its internal ksm_test_exit checks. So that when a task is killed by OOM killer or the user, KSM will not indefinitely prevent it from running exit_mmap to release its memory. This does break a part of what "ksm: fix oom deadlock" was trying to achieve. When unmerging KSM (echo 2 >/sys/kernel/mm/ksm), and even when ksmd itself has to cancel a KSM page, it is possible that the first OOM-kill victim would be the KSM process being faulted: then its memory won't be freed until a second victim has been selected (freeing memory for the unmerging fault to complete). But the OOM killer is already liable to kill a second victim once the intended victim's p->mm goes to NULL: so there's not much point in rejecting this KSM patch before fixing that OOM behaviour. It is very much more important to allow KSM users to boot up, than to haggle over an unlikely and poorly supported OOM case. We also intend to fix munlocking to not fault pages: at which point this patch _could_ be reverted; though that would be controversial, so we hope to find a better solution. Signed-off-by:Andrea Arcangeli <aarcange@redhat.com> Acked-by:
Justin M. Forbes <jforbes@redhat.com> Acked-for-now-by:
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Hugh Dickins authored
There's a now-obvious deadlock in KSM's out-of-memory handling: imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex, trying to allocate a page to break KSM in an mm which becomes the OOM victim (quite likely in the unmerge case): it's killed and goes to exit, and hangs there waiting to acquire ksm_thread_mutex. Clearly we must not require ksm_thread_mutex in __ksm_exit, simple though that made everything else: perhaps use mmap_sem somehow? And part of the answer lies in the comments on unmerge_ksm_pages: __ksm_exit should also leave all the rmap_item removal to ksmd. But there's a fundamental problem, that KSM relies upon mmap_sem to guarantee the consistency of the mm it's dealing with, yet exit_mmap tears down an mm without taking mmap_sem. And bumping mm_users won't help at all, that just ensures that the pages the OOM killer assumes are on their way to being freed will not be freed. The best answer seems to be, to move the ksm_exit callout from just before exit_mmap, to the middle of exit_mmap: after the mm's pages have been freed (if the mmu_gather is flushed), but before its page tables and vma structures have been freed; and down_write,up_write mmap_sem there to serialize with KSM's own reliance on mmap_sem. But KSM then needs to be careful, whenever it downs mmap_sem, to check that the mm is not already exiting: there's a danger of using find_vma on a layout that's being torn apart, or writing into page tables which have been freed for reuse; and even do_anonymous_page and __do_fault need to check they're not being called by break_ksm to reinstate a pte after zap_pte_range has zapped that page table. Though it might be clearer to add an exiting flag, set while holding mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating a zapped pte. All we need is to check whether mm_users is 0 - but must remember that ksmd may detect that before __ksm_exit is reached. So, ksm_test_exit(mm) added to comment such checks on mm->mm_users. __ksm_exit now has to leave clearing up the rmap_items to ksmd, that needs ksm_thread_mutex; but shift the exiting mm just after the ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise mm_count to hold the mm_struct, ksmd's exit processing (exactly like its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it, similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd). But also give __ksm_exit a fast path: when there's no complication (no rmap_items attached to mm and it's not at the ksm_scan cursor), it can safely do all the exiting work itself. This is not just an optimization: when ksmd is not running, the raised mm_count would otherwise leak mm_structs. Signed-off-by:
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Hugh Dickins authored
Do some housekeeping in ksm.c, to help make the next patch easier to understand: remove the function remove_mm_from_lists, distributing its code to its callsites scan_get_next_rmap_item and __ksm_exit. That turns out to be a win in scan_get_next_rmap_item: move its remove_trailing_rmap_items and cursor advancement up, and it becomes simpler than before. __ksm_exit becomes messier, but will change again; and moving its remove_trailing_rmap_items up lets us strengthen the unstable tree item's age condition in remove_rmap_item_from_tree. Signed-off-by:
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Hugh Dickins authored
break_ksm has been looping endlessly ignoring VM_FAULT_OOM: that should only be a problem for ksmd when a memory control group imposes limits (normally the OOM killer will kill others with an mm until it succeeds); but in general (especially for MADV_UNMERGEABLE and KSM_RUN_UNMERGE) we do need to route the error (or kill) back to the caller (or sighandling). Test signal_pending in unmerge_ksm_pages, which could be a lengthy procedure if it has to spill into swap: returning -ERESTARTSYS so that trivial signals will restart but fatals will terminate (is that right? we do different things in different places in mm, none exactly this). unmerge_and_remove_all_rmap_items was forgetting to lock when going down the mm_list: fix that. Whether it's successful or not, reset ksm_scan cursor to head; but only if it's successful, reset seqnr (shown in full_scans) - page counts will have gone down to zero. This patch leaves a significant OOM deadlock, but it's a good step on the way, and that deadlock is fixed in a subsequent patch. Signed-off-by:
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Hugh Dickins authored
1. We don't use __break_cow entry point now: merge it into break_cow. 2. remove_all_slot_rmap_items is just a special case of remove_trailing_rmap_items: use the latter instead. 3. Extend comment on unmerge_ksm_pages and rmap_items. 4. try_to_merge_two_pages should use try_to_merge_with_ksm_page instead of duplicating its code; and so swap them around. 5. Comment on cmp_and_merge_page described last year's: update it. Signed-off-by:
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Hugh Dickins authored
ksm_scan_thread already sleeps in wait_event_interruptible until setting ksm_run activates it; but if there's nothing on its list to look at, i.e. nobody has yet said madvise MADV_MERGEABLE, it's a shame to be clocking up system time and full_scans: ksmd_should_run added to check that too. And move the mutex_lock out around it: the new counts showed that when ksm_run is stopped, a little work often got done afterwards, because it had been read before taking the mutex. Signed-off-by:
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Hugh Dickins authored
We kept agreeing not to bother about the unswappable shared KSM pages which later become unshared by others: observation suggests they're not a significant proportion. But they are disadvantageous, and it is easier to break COW to replace them by swappable pages, than offer statistics to show that they don't matter; then we can stop worrying about them. Doing this in ksm_do_scan, they don't go through cmp_and_merge_page on this pass: give them a good chance of getting into the unstable tree on the next pass, or back into the stable, by computing checksum now. Signed-off-by:
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Hugh Dickins authored
The pages_shared and pages_sharing counts give a good picture of how successful KSM is at sharing; but no clue to how much wasted work it's doing to get there. Add pages_unshared (count of unique pages waiting in the unstable tree, hoping to find a mate) and pages_volatile. pages_volatile is harder to define. It includes those pages changing too fast to get into the unstable tree, but also whatever other edge conditions prevent a page getting into the trees: a high value may deserve investigation. Don't try to calculate it from the various conditions: it's the total of rmap_items less those accounted for. Also show full_scans: the number of completed scans of everything registered in the mm list. The locking for all these counts is simply ksm_thread_mutex. Signed-off-by:
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Hugh Dickins authored
The pages_shared count is incremented and decremented when adding a node to and removing a node from the stable tree: easy to understand. But the pages_sharing count was hard to follow, being adjusted in various places: increment and decrement it when adding to and removing from the stable tree. And the pages_sharing variable used to include the pages_shared, then those were subtracted when shown in the pages_sharing sysfs file: now keep it as an exclusive count of leaves hanging off the stable tree nodes, throughout. Signed-off-by:
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Hugh Dickins authored
We're not implementing swapping of KSM pages in its first release; but when that follows, "kernel_pages_allocated" will be a very poor name for the sysfs file showing number of nodes in the stable tree: rename that to "pages_shared" throughout. But we already have a "pages_shared", counting those page slots sharing the shared pages: first rename that to... "pages_sharing". What will become of "max_kernel_pages" when the pages shared can be swapped? I guess it will just be removed, so keep that name. Signed-off-by:
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Izik Eidus authored
ksm should try not to disturb other tasks as much as possible. Signed-off-by:
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Izik Eidus authored
Adding Hugh Dickins into the authors list. Signed-off-by:
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Hugh Dickins authored
KSM's scan allows for user pages to be COWed or unmapped at any time, without requiring any notification. But its stable tree does assume that when it finds a KSM page where it placed a KSM page, then it is the same KSM page that it placed there. mremap move could break that assumption: if an area containing a KSM page was unmapped, then an area containing a different KSM page was moved with mremap into the place of the original, before KSM's scan came around to notice. That could then poison a node of the stable tree, so that memcmps would "lie" and upset the ordering of the tree. Probably noone will ever need mremap move on a VM_MERGEABLE area; except that prohibiting it would make trouble for schemes in which we try making everything VM_MERGEABLE e.g. for testing: an mremap which normally works would then fail mysteriously. There's no need to go to any trouble, such as re-sorting KSM's list of rmap_items to match the new layout: simply unmerge the area to COW all its KSM pages before moving, but leave VM_MERGEABLE on so that they're remerged later. Signed-off-by:
Chris Wright <chrisw@redhat.com> Signed-off-by:
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Izik Eidus authored
Ksm is code that allows merging of identical pages between one or more applications, in a way invisible to the applications that use it. Pages that are merged are marked as read-only, then COWed when any application tries to change them. Whereas fork() allows sharing anonymous pages between parent and child, ksm can share anonymous pages between unrelated processes. Ksm works by walking over the memory pages of the applications it scans, in order to find identical pages. It uses two sorted data structures, called the stable and unstable trees, to locate identical pages in an effective way. When ksm finds two identical pages, it marks them as readonly and merges them into a single page. After the pages have been marked as readonly and merged into one, Linux treats them as normal copy-on-write pages, copying to a fresh anonymous page if write access is required later. Ksm scans and merges anonymous pages only in those memory areas that have been registered with it by madvise(addr, length, MADV_MERGEABLE). The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/: max_kernel_pages - the maximum number of unswappable kernel pages which may be allocated by ksm (0 for unlimited). kernel_pages_allocated - how many ksm pages are currently allocated, sharing identical content between different processes (pages unswappable in this release). pages_shared - how many pages have been saved by sharing with ksm pages (kernel_pages_allocated being excluded from this count). pages_to_scan - how many pages ksm should scan before sleeping. sleep_millisecs - how many milliseconds ksm should sleep between scans. run - write 0 to disable ksm, read 0 while ksm is disabled (default), write 1 to run ksm, read 1 while ksm is running, write 2 to disable ksm and unmerge all its pages. Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins. [hugh.dickins@tiscali.co.uk: fix rare page leak] Signed-off-by: -
Hugh Dickins authored
KSM will need to identify its kernel merged pages unambiguously, and /proc/kpageflags will probably like to do so too. Since KSM will only be substituting anonymous pages, statistics are best preserved by making a PageKsm page a special PageAnon page: one with no anon_vma. But KSM then needs its own page_add_ksm_rmap() - keep it in ksm.h near PageKsm; and do_wp_page() must COW them, unlike singly mapped PageAnons. Signed-off-by:
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Hugh Dickins authored
page_dup_rmap(), used on each mapped page when forking, was originally just an inline atomic_inc of mapcount. 2.6.22 added CONFIG_DEBUG_VM out-of-line checks to it, which would need to be ever-so-slightly complicated to allow for the PageKsm() we're about to define. But I think these checks never caught anything. And if it's coding errors we're worried about, such checks should be in page_remove_rmap() too, not just when forking; whereas if it's pagetable corruption we're worried about, then they shouldn't be limited to CONFIG_DEBUG_VM. Oh, just revert page_dup_rmap() to an inline atomic_inc of mapcount. Signed-off-by:
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Hugh Dickins authored
This patch presents the mm interface to a dummy version of ksm.c, for better scrutiny of that interface: the real ksm.c follows later. When CONFIG_KSM is not set, madvise(2) reject MADV_MERGEABLE and MADV_UNMERGEABLE with EINVAL, since that seems more helpful than pretending that they can be serviced. But when CONFIG_KSM=y, accept them even if KSM is not currently running, and even on areas which KSM will not touch (e.g. hugetlb or shared file or special driver mappings). Like other madvices, report ENOMEM despite success if any area in the range is unmapped, and use EAGAIN to report out of memory. Define vma flag VM_MERGEABLE to identify an area on which KSM may try merging pages: leave it to ksm_madvise() to decide whether to set it. Define mm flag MMF_VM_MERGEABLE to identify an mm which might contain VM_MERGEABLE areas, to minimize callouts when forking or exiting. Based upon earlier patches by Chris Wright and Izik Eidus. Signed-off-by:
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Hugh Dickins authored
The out-of-tree KSM used ioctls on fds cloned from /dev/ksm to register a memory area for merging: we prefer now to use an madvise(2) interface. This patch just defines MADV_MERGEABLE (to tell KSM it may merge pages in this area found identical to pages in other mergeable areas) and MADV_UNMERGEABLE (to undo that). Most architectures use asm-generic, but alpha, mips, parisc, xtensa need their own definitions: included here for mmotm convenience, but we'll probably want to split this and feed pieces to arch maintainers. Based upon earlier patches by Chris Wright and Izik Eidus. Signed-off-by:
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Hugh Dickins authored
madvise.c has several levels of switch statements, what to do in which? Move MADV_DOFORK code down from madvise_vma() to madvise_behavior(), so madvise_vma() can be a simple router, to madvise_behavior() by default. vma->vm_flags is an unsigned long so use the same type for new_flags. Add missing comment lines to describe MADV_DONTFORK and MADV_DOFORK. Signed-off-by:
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Izik Eidus authored
KSM is a linux driver that allows dynamicly sharing identical memory pages between one or more processes. Unlike tradtional page sharing that is made at the allocation of the memory, ksm do it dynamicly after the memory was created. Memory is periodically scanned; identical pages are identified and merged. The sharing is made in a transparent way to the processes that use it. Ksm is highly important for hypervisors (kvm), where in production enviorments there might be many copys of the same data data among the host memory. This kind of data can be: similar kernels, librarys, cache, and so on. Even that ksm was wrote for kvm, any userspace application that want to use it to share its data can try it. Ksm may be useful for any application that might have similar (page aligment) data strctures among the memory, ksm will find this data merge it to one copy, and even if it will be changed and thereforew copy on writed, ksm will merge it again as soon as it will be identical again. Another reason to consider using ksm is the fact that it might simplify alot the userspace code of application that want to use shared private data, instead that the application will mange shared area, ksm will do this for the application, and even write to this data will be allowed without any synchinization acts from the application. Ksm was designed to be a loadable module that doesn't change the VM code of linux. This patch: The set_pte_at_notify() macro allows setting a pte in the shadow page table directly, instead of flushing the shadow page table entry and then getting vmexit to set it. It uses a new change_pte() callback to do so. set_pte_at_notify() is an optimization for kvm, and other users of mmu_notifiers, for COW pages. It is useful for kvm when ksm is used, because it allows kvm not to have to receive vmexit and only then map the ksm page into the shadow page table, but instead map it directly at the same time as Linux maps the page into the host page table. Users of mmu_notifiers who don't implement new mmu_notifier_change_pte() callback will just receive the mmu_notifier_invalidate_page() callback. Signed-off-by:
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Johannes Weiner authored
By the time PG_mlocked is cleared in the page freeing path, nobody else is looking at our page->flags anymore. It is thus safe to make the test-and-clear non-atomic and thereby removing an unnecessary and expensive operation from a hotpath. Signed-off-by:
Johannes Weiner <hannes@cmpxchg.org> Reviewed-by:
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Figo.zhang authored
There is no need for double error checking. Signed-off-by:
Figo.zhang <figo1802@gmail.com> Acked-by:
Tejun Heo <tj@kernel.org> Signed-off-by:
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Akinobu Mita authored
__get_free_pages() with __GFP_HIGHMEM is not safe because the return address cannot represent a highmem page. get_zeroed_page() already has such a debug checking. Signed-off-by:
Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by:
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KOSAKI Motohiro authored
The pages in the list passed move_active_pages_to_lru() are already touched by shrink_active_list(). IOW the prefetch in move_active_pages_to_lru() don't populate any cache. it's pointless. This patch remove it. Signed-off-by:
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