- 22 Jan, 2014 40 commits
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Oleg Nesterov authored
Change oom_kill.c to use for_each_thread() rather than the racy while_each_thread() which can loop forever if we race with exit. Note also that most users were buggy even if while_each_thread() was fine, the task can exit even _before_ rcu_read_lock(). Fortunately the new for_each_thread() only requires the stable task_struct, so this change fixes both problems. Signed-off-by:
Oleg Nesterov <oleg@redhat.com> Reviewed-by:
Sergey Dyasly <dserrg@gmail.com> Tested-by:
Sameer Nanda <snanda@chromium.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Mandeep Singh Baines <msb@chromium.org> Cc: "Ma, Xindong" <xindong.ma@intel.com> Reviewed-by:
Michal Hocko <mhocko@suse.cz> Cc: "Tu, Xiaobing" <xiaobing.tu@intel.com> Acked-by:
David Rientjes <rientjes@google.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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Oleg Nesterov authored
while_each_thread() and next_thread() should die, almost every lockless usage is wrong. 1. Unless g == current, the lockless while_each_thread() is not safe. while_each_thread(g, t) can loop forever if g exits, next_thread() can't reach the unhashed thread in this case. Note that this can happen even if g is the group leader, it can exec. 2. Even if while_each_thread() itself was correct, people often use it wrongly. It was never safe to just take rcu_read_lock() and loop unless you verify that pid_alive(g) == T, even the first next_thread() can point to the already freed/reused memory. This patch adds signal_struct->thread_head and task->thread_node to create the normal rcu-safe list with the stable head. The new for_each_thread(g, t) helper is always safe under rcu_read_lock() as long as this task_struct can't go away. Note: of course it is ugly to have both task_struct->thread_node and the old task_struct->thread_group, we will kill it later, after we change the users of while_each_thread() to use for_each_thread(). Perhaps we can kill it even before we convert all users, we can reimplement next_thread(t) using the new thread_head/thread_node. But we can't do this right now because this will lead to subtle behavioural changes. For example, do/while_each_thread() always sees at least one task, while for_each_thread() can do nothing if the whole thread group has died. Or thread_group_empty(), currently its semantics is not clear unless thread_group_leader(p) and we need to audit the callers before we can change it. So this patch adds the new interface which has to coexist with the old one for some time, hopefully the next changes will be more or less straightforward and the old one will go away soon. Signed-off-by:
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Joonsoo Kim authored
Now, we have an infrastructure in rmap_walk() to handle difference from variants of rmap traversing functions. So, just use it in page_mkclean(). In this patch, I change following things. 1. remove some variants of rmap traversing functions. cf> page_mkclean_file 2. mechanical change to use rmap_walk() in page_mkclean(). Signed-off-by:Joonsoo Kim <iamjoonsoo.kim@lge.com> Reviewed-by:
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Hillf Danton <dhillf@gmail.com> Signed-off-by:
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Joonsoo Kim authored
Now, we have an infrastructure in rmap_walk() to handle difference from variants of rmap traversing functions. So, just use it in page_referenced(). In this patch, I change following things. 1. remove some variants of rmap traversing functions. cf> page_referenced_ksm, page_referenced_anon, page_referenced_file 2. introduce new struct page_referenced_arg and pass it to page_referenced_one(), main function of rmap_walk, in order to count reference, to store vm_flags and to check finish condition. 3. mechanical change to use rmap_walk() in page_referenced(). [liwanp@linux.vnet.ibm.com: fix BUG at rmap_walk] Signed-off-by:
Wanpeng Li <liwanp@linux.vnet.ibm.com> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by:
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Joonsoo Kim authored
Now, we have an infrastructure in rmap_walk() to handle difference from variants of rmap traversing functions. So, just use it in try_to_munlock(). In this patch, I change following things. 1. remove some variants of rmap traversing functions. cf> try_to_unmap_ksm, try_to_unmap_anon, try_to_unmap_file 2. mechanical change to use rmap_walk() in try_to_munlock(). 3. copy and paste comments. Signed-off-by:
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Joonsoo Kim authored
Now, we have an infrastructure in rmap_walk() to handle difference from variants of rmap traversing functions. So, just use it in try_to_unmap(). In this patch, I change following things. 1. enable rmap_walk() if !CONFIG_MIGRATION. 2. mechanical change to use rmap_walk() in try_to_unmap(). Signed-off-by:
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Joonsoo Kim authored
There are a lot of common parts in traversing functions, but there are also a little of uncommon parts in it. By assigning proper function pointer on each rmap_walker_control, we can handle these difference correctly. Following are differences we should handle. 1. difference of lock function in anon mapping case 2. nonlinear handling in file mapping case 3. prechecked condition: checking memcg in page_referenced(), checking VM_SHARE in page_mkclean() checking temporary vma in try_to_unmap() 4. exit condition: checking page_mapped() in try_to_unmap() So, in this patch, I introduce 4 function pointers to handle above differences. Signed-off-by:
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Joonsoo Kim authored
In each rmap traverse case, there is some difference so that we need function pointers and arguments to them in order to handle these For this purpose, struct rmap_walk_control is introduced in this patch, and will be extended in following patch. Introducing and extending are separate, because it clarify changes. Signed-off-by:
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Joonsoo Kim authored
When we traverse anon_vma, we need to take a read-side anon_lock. But there is subtle difference in the situation so that we can't use same method to take a lock in each cases. Therefore, we need to make rmap_walk_anon() taking difference lock function. This patch is the first step, factoring lock function for anon_lock out of rmap_walk_anon(). It will be used in case of removing migration entry and in default of rmap_walk_anon(). Signed-off-by:
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Joonsoo Kim authored
To merge all kinds of rmap traverse functions, try_to_unmap(), try_to_munlock(), page_referenced() and page_mkclean(), we need to extract common parts and separate out non-common parts. Nonlinear handling is handled just in try_to_unmap_file() and other rmap traverse functions doesn't care of it. Therfore it is better to factor nonlinear handling out of try_to_unmap_file() in order to merge all kinds of rmap traverse functions easily. Signed-off-by:
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Joonsoo Kim authored
Rmap traversing is used in five different cases, try_to_unmap(), try_to_munlock(), page_referenced(), page_mkclean() and remove_migration_ptes(). Each one implements its own traversing functions for the cases, anon, file, ksm, respectively. These cause lots of duplications and cause maintenance overhead. They also make codes being hard to understand and error-prone. One example is hugepage handling. There is a code to compute hugepage offset correctly in try_to_unmap_file(), but, there isn't a code to compute hugepage offset in rmap_walk_file(). These are used pairwise in migration context, but we missed to modify pairwise. To overcome these drawbacks, we should unify these through one unified function. I decide rmap_walk() as main function since it has no unnecessity. And to control behavior of rmap_walk(), I introduce struct rmap_walk_control having some function pointers. These makes rmap_walk() working for their specific needs. This patchset remove a lot of duplicated code as you can see in below short-stat and kernel text size also decrease slightly. text data bss dec hex filename 10640 1 16 10657 29a1 mm/rmap.o 10047 1 16 10064 2750 mm/rmap.o 13823 705 8288 22816 5920 mm/ksm.o 13199 705 8288 22192 56b0 mm/ksm.o This patch (of 9): We have to recompute pgoff if the given page is huge, since result based on HPAGE_SIZE is not approapriate for scanning the vma interval tree, as shown by commit 36e4f20a ("hugetlb: do not use vma_hugecache_offset() for vma_prio_tree_foreach") and commit 369a713e ("rmap: recompute pgoff for unmapping huge page"). To handle both the cases, normal page for page cache and hugetlb page, by same way, we can use compound_page(). It returns 0 on non-compound page and it also returns proper value on compound page. Signed-off-by:
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Vladimir Davydov authored
This function is not used outside of memcontrol.c so make it static. Signed-off-by:
Vladimir Davydov <vdavydov@parallels.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Acked-by:
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Vladimir Davydov authored
We should start kmem accounting for a memory cgroup only after both its kmem limit is set (KMEM_ACCOUNTED_ACTIVE) and related call sites are patched (KMEM_ACCOUNTED_ACTIVATED). Currently memcg_can_account_kmem() allows kmem accounting even if only one of the conditions is true. Fix it. This means that a page might get charged by memcg_kmem_newpage_charge which would see its static key patched already but memcg_kmem_commit_charge would still see it unpatched and so the charge won't be committed. The result would be charge inconsistency (page_cgroup not marked as PageCgroupUsed) and the charge would leak because __memcg_kmem_uncharge_pages would ignore it. [mhocko@suse.cz: augment changelog] Signed-off-by:
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Tang Chen authored
If users specify the original movablecore=nn@ss boot option, the kernel will arrange [ss, ss+nn) as ZONE_MOVABLE. The kernelcore=nn@ss boot option is similar except it specifies ZONE_NORMAL ranges. Now, if users specify "movable_node" in kernel commandline, the kernel will arrange hotpluggable memory in SRAT as ZONE_MOVABLE. And if users do this, all the other movablecore=nn@ss and kernelcore=nn@ss options should be ignored. For those who don't want this, just specify nothing. The kernel will act as before. Signed-off-by:
Tang Chen <tangchen@cn.fujitsu.com> Signed-off-by:
Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Reviewed-by:
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Tang Chen authored
Linux kernel cannot migrate pages used by the kernel. As a result, hotpluggable memory used by the kernel won't be able to be hot-removed. To solve this problem, the basic idea is to prevent memblock from allocating hotpluggable memory for the kernel at early time, and arrange all hotpluggable memory in ACPI SRAT(System Resource Affinity Table) as ZONE_MOVABLE when initializing zones. In the previous patches, we have marked hotpluggable memory regions with MEMBLOCK_HOTPLUG flag in memblock.memory. In this patch, we make memblock skip these hotpluggable memory regions in the default top-down allocation function if movable_node boot option is specified. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by:
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Tang Chen authored
At very early time, the kernel have to use some memory such as loading the kernel image. We cannot prevent this anyway. So any node the kernel resides in should be un-hotpluggable. Signed-off-by:
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Tang Chen authored
When parsing SRAT, we know that which memory area is hotpluggable. So we invoke function memblock_mark_hotplug() introduced by previous patch to mark hotpluggable memory in memblock. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by:
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Tang Chen authored
[sfr@canb.auug.org.au: fix powerpc build] Signed-off-by:
Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by:
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Tang Chen authored
In find_hotpluggable_memory, once we find out a memory region which is hotpluggable, we want to mark them in memblock.memory. So that we could control memblock allocator not to allocte hotpluggable memory for the kernel later. To achieve this goal, we introduce MEMBLOCK_HOTPLUG flag to indicate the hotpluggable memory regions in memblock and a function memblock_mark_hotplug() to mark hotpluggable memory if we find one. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by:
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Tang Chen authored
There is no flag in memblock to describe what type the memory is. Sometimes, we may use memblock to reserve some memory for special usage. And we want to know what kind of memory it is. So we need a way to In hotplug environment, we want to reserve hotpluggable memory so the kernel won't be able to use it. And when the system is up, we have to free these hotpluggable memory to buddy. So we need to mark these memory first. In order to do so, we need to mark out these special memory in memblock. In this patch, we introduce a new "flags" member into memblock_region: struct memblock_region { phys_addr_t base; phys_addr_t size; unsigned long flags; /* This is new. */ #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP int nid; #endif }; This patch does the following things: 1) Add "flags" member to memblock_region. 2) Modify the following APIs' prototype: memblock_add_region() memblock_insert_region() 3) Add memblock_reserve_region() to support reserve memory with flags, and keep memblock_reserve()'s prototype unmodified. 4) Modify other APIs to support flags, but keep their prototype unmodified. The idea is from Wen Congyang <wency@cn.fujitsu.com> and Liu Jiang <jiang.liu@huawei.com>. Suggested-by:Wen Congyang <wency@cn.fujitsu.com> Suggested-by:
Liu Jiang <jiang.liu@huawei.com> Signed-off-by:
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Grygorii Strashko authored
Current memblock APIs don't work on 32 PAE or LPAE extension arches where the physical memory start address beyond 4GB. The problem was discussed here [3] where Tejun, Yinghai(thanks) proposed a way forward with memblock interfaces. Based on the proposal, this series adds necessary memblock interfaces and convert the core kernel code to use them. Architectures already converted to NO_BOOTMEM use these new interfaces and other which still uses bootmem, these new interfaces just fallback to exiting bootmem APIs. So no functional change in behavior. In long run, once all the architectures moves to NO_BOOTMEM, we can get rid of bootmem layer completely. This is one step to remove the core code dependency with bootmem and also gives path for architectures to move away from bootmem. Testing is done on ARM architecture with 32 bit ARM LAPE machines with normal as well sparse(faked) memory model. This patch (of 23): When debugging is enabled (cmdline has "memblock=debug") the memblock will display upper memory boundary per each allocated/freed memory range wrongly. For example: memblock_reserve: [0x0000009e7e8000-0x0000009e7ed000] _memblock_early_alloc_try_nid_nopanic+0xfc/0x12c The 0x0000009e7ed000 is displayed instead of 0x0000009e7ecfff Hence, correct this by changing formula used to calculate upper memory boundary to (u64)base + size - 1 instead of (u64)base + size everywhere in the debug messages. Signed-off-by:
Grygorii Strashko <grygorii.strashko@ti.com> Signed-off-by:
Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Yinghai Lu <yinghai@kernel.org> Acked-by:
Tejun Heo <tj@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Russell King <linux@arm.linux.org.uk> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Paul Walmsley <paul@pwsan.com> Cc: Pavel Machek <pavel@ucw.cz> Cc: Tony Lindgren <tony@atomide.com> Signed-off-by:
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Davidlohr Bueso authored
All mlock related syscalls prepare lock limits, lengths and start parameters with the mmap_sem held. Move this logic outside of the critical region. For the case of mlock, continue incrementing the amount already locked by mm->locked_vm with the rwsem taken. Signed-off-by:
Davidlohr Bueso <davidlohr@hp.com> Cc: Rik van Riel <riel@redhat.com> Reviewed-by:
Michel Lespinasse <walken@google.com> Acked-by:
Vlastimil Babka <vbabka@suse.cz> Signed-off-by:
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Davidlohr Bueso authored
Both do_brk and do_mmap_pgoff verify that we are actually capable of locking future pages if the corresponding VM_LOCKED flags are used. Encapsulate this logic into a single mlock_future_check() helper function. Signed-off-by:
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Jerome Marchand authored
Some applications that run on HPC clusters are designed around the availability of RAM and the overcommit ratio is fine tuned to get the maximum usage of memory without swapping. With growing memory, the 1%-of-all-RAM grain provided by overcommit_ratio has become too coarse for these workload (on a 2TB machine it represents no less than 20GB). This patch adds the new overcommit_kbytes sysctl variable that allow a much finer grain. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: fix nommu build] Signed-off-by:
Jerome Marchand <jmarchan@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by:
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Mel Gorman authored
Commit 4b59e6c4 ("mm, show_mem: suppress page counts in non-blockable contexts") introduced SHOW_MEM_FILTER_PAGE_COUNT to suppress PFN walks on large memory machines. Commit c78e9363 ("mm: do not walk all of system memory during show_mem") avoided a PFN walk in the generic show_mem helper which removes the requirement for SHOW_MEM_FILTER_PAGE_COUNT in that case. This patch removes PFN walkers from the arch-specific implementations that report on a per-node or per-zone granularity. ARM and unicore32 still do a PFN walk as they report memory usage on each bank which is a much finer granularity where the debugging information may still be of use. As the remaining arches doing PFN walks have relatively small amounts of memory, this patch simply removes SHOW_MEM_FILTER_PAGE_COUNT. [akpm@linux-foundation.org: fix parisc] Signed-off-by:
Mel Gorman <mgorman@suse.de> Acked-by:
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Jianyu Zhan authored
Currently we are implementing vmalloc_to_pfn() as a wrapper around vmalloc_to_page(), which is implemented as follow: 1. walks the page talbes to generates the corresponding pfn, 2. then converts the pfn to struct page, 3. returns it. And vmalloc_to_pfn() re-wraps vmalloc_to_page() to get the pfn. This seems too circuitous, so this patch reverses the way: implement vmalloc_to_page() as a wrapper around vmalloc_to_pfn(). This makes vmalloc_to_pfn() and vmalloc_to_page() slightly more efficient. No functional change. Signed-off-by:
Jianyu Zhan <nasa4836@gmail.com> Cc: Vladimir Murzin <murzin.v@gmail.com> Signed-off-by:
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David Rientjes authored
Mempolicies only exist for CONFIG_NUMA configurations. Therefore, a certain class of functions are unneeded in configurations where CONFIG_NUMA is disabled such as functions that duplicate existing mempolicies, lookup existing policies, set certain mempolicy traits, or test mempolicies for certain attributes. Remove the unneeded functions so that any future callers get a compile- time error and protect their code with CONFIG_NUMA as required. Signed-off-by:
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Andreas Sandberg authored
When copy_hugetlb_page_range() is called to copy a range of hugetlb mappings, the secondary MMUs are not notified if there is a protection downgrade, which breaks COW semantics in KVM. This patch adds the necessary MMU notifier calls. Signed-off-by:
Andreas Sandberg <andreas@sandberg.pp.se> Acked-by:
Steve Capper <steve.capper@linaro.org> Acked-by:
Marc Zyngier <marc.zyngier@arm.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:
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Zhi Yong Wu authored
[akpm@linux-foundation.org: s/cache/pagecache/] Signed-off-by:
Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> Signed-off-by:
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Kirill A. Shutemov authored
If DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC are enabled spinlock_t on x86_64 is 72 bytes. For page->ptl they will be allocated from kmalloc-96 slab, so we loose 24 on each. An average system can easily allocate few tens thousands of page->ptl and overhead is significant. Let's create a separate slab for page->ptl allocation to solve this. To make sure that it really works this time, some numbers from my test machine (just booted, no load): Before: # grep '^\(kmalloc-96\|page->ptl\)' /proc/slabinfo kmalloc-96 31987 32190 128 30 1 : tunables 120 60 8 : slabdata 1073 1073 92 After: # grep '^\(kmalloc-96\|page->ptl\)' /proc/slabinfo page->ptl 27516 28143 72 53 1 : tunables 120 60 8 : slabdata 531 531 9 kmalloc-96 3853 5280 128 30 1 : tunables 120 60 8 : slabdata 176 176 0 Note that the patch is useful not only for debug case, but also for PREEMPT_RT, where spinlock_t is always bloated. Signed-off-by:
Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by:
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Yasuaki Ishimatsu authored
Yasuaki Ishimatsu reported memory hot-add spent more than 5 _hours_ on 9TB memory machine since onlining memory sections is too slow. And we found out setup_zone_migrate_reserve spent >90% of the time. The problem is, setup_zone_migrate_reserve scans all pageblocks unconditionally, but it is only necessary if the number of reserved block was reduced (i.e. memory hot remove). Moreover, maximum MIGRATE_RESERVE per zone is currently 2. It means that the number of reserved pageblocks is almost always unchanged. This patch adds zone->nr_migrate_reserve_block to maintain the number of MIGRATE_RESERVE pageblocks and it reduces the overhead of setup_zone_migrate_reserve dramatically. The following table shows time of onlining a memory section. Amount of memory | 128GB | 192GB | 256GB| --------------------------------------------- linux-3.12 | 23.9 | 31.4 | 44.5 | This patch | 8.3 | 8.3 | 8.6 | Mel's proposal patch | 10.9 | 19.2 | 31.3 | --------------------------------------------- (millisecond) 128GB : 4 nodes and each node has 32GB of memory 192GB : 6 nodes and each node has 32GB of memory 256GB : 8 nodes and each node has 32GB of memory (*1) Mel proposed his idea by the following threads. https://lkml.org/lkml/2013/10/30/272 [akpm@linux-foundation.org: tweak comment] Signed-off-by:KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by:
Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Reported-by:
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Rik van Riel authored
Many load balancing and workload placing programs check /proc/meminfo to estimate how much free memory is available. They generally do this by adding up "free" and "cached", which was fine ten years ago, but is pretty much guaranteed to be wrong today. It is wrong because Cached includes memory that is not freeable as page cache, for example shared memory segments, tmpfs, and ramfs, and it does not include reclaimable slab memory, which can take up a large fraction of system memory on mostly idle systems with lots of files. Currently, the amount of memory that is available for a new workload, without pushing the system into swap, can be estimated from MemFree, Active(file), Inactive(file), and SReclaimable, as well as the "low" watermarks from /proc/zoneinfo. However, this may change in the future, and user space really should not be expected to know kernel internals to come up with an estimate for the amount of free memory. It is more convenient to provide such an estimate in /proc/meminfo. If things change in the future, we only have to change it in one place. Signed-off-by:
Rik van Riel <riel@redhat.com> Reported-by:
Erik Mouw <erik.mouw_2@nxp.com> Acked-by:
Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:
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Oleg Nesterov authored
get_huge_page_tail()->compound_head() looks confusing. Every caller must check PageTail(page), otherwise atomic_inc(&page->_mapcount) is simply wrong if this page is compound-trans-head. Signed-off-by:
Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:
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Oleg Nesterov authored
Cleanup. Change __get_page_tail_foll() to use get_huge_page_tail() to avoid the code duplication. Signed-off-by:
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Andrea Arcangeli authored
No actual need of it. So keep it internal. Signed-off-by:
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Andrew Morton authored
Tweak it so save a tab stop, make code layout slightly less nutty. Signed-off-by:
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Andrew Morton authored
Signed-off-by:
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Andrea Arcangeli authored
Also remove hugetlb.h which isn't needed anymore as PageHeadHuge is handled in mm.h. Signed-off-by:
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Andrea Arcangeli authored
This skips the _mapcount mangling for slab and hugetlbfs pages. The main trouble in doing this is to guarantee that PageSlab and PageHeadHuge remains constant for all get_page/put_page run on the tail of slab or hugetlbfs compound pages. Otherwise if they're set during get_page but not set during put_page, the _mapcount of the tail page would underflow. PageHeadHuge will remain true until the compound page is released and enters the buddy allocator so it won't risk to change even if the tail page is the last reference left on the page. PG_slab instead is cleared before the slab frees the head page with put_page, so if the tail pin is released after the slab freed the page, we would have a problem. But in the slab case the tail pin cannot be the last reference left on the page. This is because the slab code is free to reuse the compound page after a kfree/kmem_cache_free without having to check if there's any tail pin left. In turn all tail pins must be always released while the head is still pinned by the slab code and so we know PG_slab will be still set too. Signed-off-by:
Khalid Aziz <khalid.aziz@oracle.com> Cc: Pravin Shelar <pshelar@nicira.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Ben Hutchings <bhutchings@solarflare.com> Cc: Christoph Lameter <cl@linux.com> Cc: Johannes Weiner <jweiner@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by:
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Andrea Arcangeli authored
Currently we don't clobber page_tail->first_page during split_huge_page, so compound_trans_head can be set to compound_head without adverse effects, and this mostly optimizes away a smp_rmb. It looks worthwhile to keep around the implementation that doesn't relay on page_tail->first_page not to be clobbered, because it would be necessary if we'll decide to enforce page->private to zero at all times whenever PG_private is not set, also for anonymous pages. For anonymous pages enforcing such an invariant doesn't matter as anonymous pages don't use page->private so we can get away with this microoptimization. Signed-off-by:
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