kernel.git/mm/slub.c, branch linux-3.6.y

slub: consider pfmemalloc_match() in get_partial_node()

2012-09-17T22:00:38Z

get_partial() is currently not checking pfmemalloc_match() meaning that it is possible for pfmemalloc pages to leak to non-pfmemalloc users. This is a problem in the following situation. Assume that there is a request from normal allocation and there are no objects in the per-cpu cache and no node-partial slab. In this case, slab_alloc enters the slow path and new_slab_objects() is called which may return a PFMEMALLOC page. As the current user is not allowed to access PFMEMALLOC page, deactivate_slab() is called ([5091b74a: mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks]) and returns an object from PFMEMALLOC page. Next time, when we get another request from normal allocation, slab_alloc() enters the slow-path and calls new_slab_objects(). In new_slab_objects(), we call get_partial() and get a partial slab which was just deactivated but is a pfmemalloc page. We extract one object from it and re-deactivate. "deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly. As a result, access to PFMEMALLOC page is not properly restricted and it can cause a performance degradation due to frequent deactivation. deactivation frequently. This patch changes get_partial_node() to take pfmemalloc_match() into account and prevents the "deactivate -> re-get in get_partial() scenario. Instead, new_slab() is called. Signed-off-by: Joonsoo Kim Acked-by: David Rientjes Signed-off-by: Mel Gorman Cc: David Miller Cc: Chuck Lever Cc: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks

2012-08-01T01:42:45Z

This patch removes the check for pfmemalloc from the alloc hotpath and puts the logic after the election of a new per cpu slab. For a pfmemalloc page we do not use the fast path but force the use of the slow path which is also used for the debug case. This has the side-effect of weakening pfmemalloc processing in the following way; 1. A process that is allocating for network swap calls __slab_alloc. pfmemalloc_match is true so the freelist is loaded and c->freelist is now pointing to a pfmemalloc page. 2. A process that is attempting normal allocations calls slab_alloc, finds the pfmemalloc page on the freelist and uses it because it did not check pfmemalloc_match() The patch allows non-pfmemalloc allocations to use pfmemalloc pages with the kmalloc slabs being the most vunerable caches on the grounds they are most likely to have a mix of pfmemalloc and !pfmemalloc requests. A later patch will still protect the system as processes will get throttled if the pfmemalloc reserves get depleted but performance will not degrade as smoothly. [mgorman@suse.de: Expanded changelog] Signed-off-by: Christoph Lameter Signed-off-by: Mel Gorman Cc: David Miller Cc: Neil Brown Cc: Peter Zijlstra Cc: Mike Christie Cc: Eric B Munson Cc: Eric Dumazet Cc: Sebastian Andrzej Siewior Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: sl[au]b: add knowledge of PFMEMALLOC reserve pages

2012-08-01T01:42:45Z

When a user or administrator requires swap for their application, they create a swap partition and file, format it with mkswap and activate it with swapon. Swap over the network is considered as an option in diskless systems. The two likely scenarios are when blade servers are used as part of a cluster where the form factor or maintenance costs do not allow the use of disks and thin clients. The Linux Terminal Server Project recommends the use of the Network Block Device (NBD) for swap according to the manual at https://sourceforge.net/projects/ltsp/files/Docs-Admin-Guide/LTSPManual.pdf/download There is also documentation and tutorials on how to setup swap over NBD at places like https://help.ubuntu.com/community/UbuntuLTSP/EnableNBDSWAP The nbd-client also documents the use of NBD as swap. Despite this, the fact is that a machine using NBD for swap can deadlock within minutes if swap is used intensively. This patch series addresses the problem. The core issue is that network block devices do not use mempools like normal block devices do. As the host cannot control where they receive packets from, they cannot reliably work out in advance how much memory they might need. Some years ago, Peter Zijlstra developed a series of patches that supported swap over an NFS that at least one distribution is carrying within their kernels. This patch series borrows very heavily from Peter's work to support swapping over NBD as a pre-requisite to supporting swap-over-NFS. The bulk of the complexity is concerned with preserving memory that is allocated from the PFMEMALLOC reserves for use by the network layer which is needed for both NBD and NFS. Patch 1 adds knowledge of the PFMEMALLOC reserves to SLAB and SLUB to preserve access to pages allocated under low memory situations to callers that are freeing memory. Patch 2 optimises the SLUB fast path to avoid pfmemalloc checks Patch 3 introduces __GFP_MEMALLOC to allow access to the PFMEMALLOC reserves without setting PFMEMALLOC. Patch 4 opens the possibility for softirqs to use PFMEMALLOC reserves for later use by network packet processing. Patch 5 only sets page->pfmemalloc when ALLOC_NO_WATERMARKS was required Patch 6 ignores memory policies when ALLOC_NO_WATERMARKS is set. Patches 7-12 allows network processing to use PFMEMALLOC reserves when the socket has been marked as being used by the VM to clean pages. If packets are received and stored in pages that were allocated under low-memory situations and are unrelated to the VM, the packets are dropped. Patch 11 reintroduces __skb_alloc_page which the networking folk may object to but is needed in some cases to propogate pfmemalloc from a newly allocated page to an skb. If there is a strong objection, this patch can be dropped with the impact being that swap-over-network will be slower in some cases but it should not fail. Patch 13 is a micro-optimisation to avoid a function call in the common case. Patch 14 tags NBD sockets as being SOCK_MEMALLOC so they can use PFMEMALLOC if necessary. Patch 15 notes that it is still possible for the PFMEMALLOC reserve to be depleted. To prevent this, direct reclaimers get throttled on a waitqueue if 50% of the PFMEMALLOC reserves are depleted. It is expected that kswapd and the direct reclaimers already running will clean enough pages for the low watermark to be reached and the throttled processes are woken up. Patch 16 adds a statistic to track how often processes get throttled Some basic performance testing was run using kernel builds, netperf on loopback for UDP and TCP, hackbench (pipes and sockets), iozone and sysbench. Each of them were expected to use the sl*b allocators reasonably heavily but there did not appear to be significant performance variances. For testing swap-over-NBD, a machine was booted with 2G of RAM with a swapfile backed by NBD. 8*NUM_CPU processes were started that create anonymous memory mappings and read them linearly in a loop. The total size of the mappings were 4*PHYSICAL_MEMORY to use swap heavily under memory pressure. Without the patches and using SLUB, the machine locks up within minutes and runs to completion with them applied. With SLAB, the story is different as an unpatched kernel run to completion. However, the patched kernel completed the test 45% faster. MICRO 3.5.0-rc2 3.5.0-rc2 vanilla swapnbd Unrecognised test vmscan-anon-mmap-write MMTests Statistics: duration Sys Time Running Test (seconds) 197.80 173.07 User+Sys Time Running Test (seconds) 206.96 182.03 Total Elapsed Time (seconds) 3240.70 1762.09 This patch: mm: sl[au]b: add knowledge of PFMEMALLOC reserve pages Allocations of pages below the min watermark run a risk of the machine hanging due to a lack of memory. To prevent this, only callers who have PF_MEMALLOC or TIF_MEMDIE set and are not processing an interrupt are allowed to allocate with ALLOC_NO_WATERMARKS. Once they are allocated to a slab though, nothing prevents other callers consuming free objects within those slabs. This patch limits access to slab pages that were alloced from the PFMEMALLOC reserves. When this patch is applied, pages allocated from below the low watermark are returned with page->pfmemalloc set and it is up to the caller to determine how the page should be protected. SLAB restricts access to any page with page->pfmemalloc set to callers which are known to able to access the PFMEMALLOC reserve. If one is not available, an attempt is made to allocate a new page rather than use a reserve. SLUB is a bit more relaxed in that it only records if the current per-CPU page was allocated from PFMEMALLOC reserve and uses another partial slab if the caller does not have the necessary GFP or process flags. This was found to be sufficient in tests to avoid hangs due to SLUB generally maintaining smaller lists than SLAB. In low-memory conditions it does mean that !PFMEMALLOC allocators can fail a slab allocation even though free objects are available because they are being preserved for callers that are freeing pages. [a.p.zijlstra@chello.nl: Original implementation] [sebastian@breakpoint.cc: Correct order of page flag clearing] Signed-off-by: Mel Gorman Cc: David Miller Cc: Neil Brown Cc: Peter Zijlstra Cc: Mike Christie Cc: Eric B Munson Cc: Eric Dumazet Cc: Sebastian Andrzej Siewior Cc: Mel Gorman Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, slub: ensure irqs are enabled for kmemcheck

2012-07-10T19:43:52Z

kmemcheck_alloc_shadow() requires irqs to be enabled, so wait to disable them until after its called for __GFP_WAIT allocations. This fixes a warning for such allocations: WARNING: at kernel/lockdep.c:2739 lockdep_trace_alloc+0x14e/0x1c0() Acked-by: Fengguang Wu Acked-by: Steven Rostedt Tested-by: Fengguang Wu Signed-off-by: David Rientjes Signed-off-by: Pekka Enberg

mm, sl[aou]b: Move kmem_cache_create mutex handling to common code

2012-07-09T09:13:42Z

Move the mutex handling into the common kmem_cache_create() function. Then we can also move more checks out of SLAB's kmem_cache_create() into the common code. Reviewed-by: Glauber Costa Signed-off-by: Christoph Lameter Signed-off-by: Pekka Enberg

mm, sl[aou]b: Use a common mutex definition

2012-07-09T09:13:41Z

Use the mutex definition from SLAB and make it the common way to take a sleeping lock. This has the effect of using a mutex instead of a rw semaphore for SLUB. SLOB gains the use of a mutex for kmem_cache_create serialization. Not needed now but SLOB may acquire some more features later (like slabinfo / sysfs support) through the expansion of the common code that will need this. Reviewed-by: Glauber Costa Reviewed-by: Joonsoo Kim Signed-off-by: Christoph Lameter Signed-off-by: Pekka Enberg

mm, sl[aou]b: Common definition for boot state of the slab allocators

2012-07-09T09:13:35Z

All allocators have some sort of support for the bootstrap status. Setup a common definition for the boot states and make all slab allocators use that definition. Reviewed-by: Glauber Costa Reviewed-by: Joonsoo Kim Signed-off-by: Christoph Lameter Signed-off-by: Pekka Enberg

mm, sl[aou]b: Extract common code for kmem_cache_create()

2012-07-09T09:13:30Z

Kmem_cache_create() does a variety of sanity checks but those vary depending on the allocator. Use the strictest tests and put them into a slab_common file. Make the tests conditional on CONFIG_DEBUG_VM. This patch has the effect of adding sanity checks for SLUB and SLOB under CONFIG_DEBUG_VM and removes the checks in SLAB for !CONFIG_DEBUG_VM. Signed-off-by: Christoph Lameter Signed-off-by: Pekka Enberg

slub: remove invalid reference to list iterator variable

2012-07-09T09:04:34Z

If list_for_each_entry, etc complete a traversal of the list, the iterator variable ends up pointing to an address at an offset from the list head, and not a meaningful structure. Thus this value should not be used after the end of the iterator. The patch replaces s->name by al->name, which is referenced nearby. This problem was found using Coccinelle (http://coccinelle.lip6.fr/). Signed-off-by: Julia Lawall Signed-off-by: Pekka Enberg

slub: refactoring unfreeze_partials()

2012-06-20T07:17:45Z

Current implementation of unfreeze_partials() is so complicated, but benefit from it is insignificant. In addition many code in do {} while loop have a bad influence to a fail rate of cmpxchg_double_slab. Under current implementation which test status of cpu partial slab and acquire list_lock in do {} while loop, we don't need to acquire a list_lock and gain a little benefit when front of the cpu partial slab is to be discarded, but this is a rare case. In case that add_partial is performed and cmpxchg_double_slab is failed, remove_partial should be called case by case. I think that these are disadvantages of current implementation, so I do refactoring unfreeze_partials(). Minimizing code in do {} while loop introduce a reduced fail rate of cmpxchg_double_slab. Below is output of 'slabinfo -r kmalloc-256' when './perf stat -r 33 hackbench 50 process 4000 > /dev/null' is done. ** before ** Cmpxchg_double Looping ------------------------ Locked Cmpxchg Double redos 182685 Unlocked Cmpxchg Double redos 0 ** after ** Cmpxchg_double Looping ------------------------ Locked Cmpxchg Double redos 177995 Unlocked Cmpxchg Double redos 1 We can see cmpxchg_double_slab fail rate is improved slightly. Bolow is output of './perf stat -r 30 hackbench 50 process 4000 > /dev/null'. ** before ** Performance counter stats for './hackbench 50 process 4000' (30 runs): 108517.190463 task-clock # 7.926 CPUs utilized ( +- 0.24% ) 2,919,550 context-switches # 0.027 M/sec ( +- 3.07% ) 100,774 CPU-migrations # 0.929 K/sec ( +- 4.72% ) 124,201 page-faults # 0.001 M/sec ( +- 0.15% ) 401,500,234,387 cycles # 3.700 GHz ( +- 0.24% ) stalled-cycles-frontend stalled-cycles-backend 250,576,913,354 instructions # 0.62 insns per cycle ( +- 0.13% ) 45,934,956,860 branches # 423.297 M/sec ( +- 0.14% ) 188,219,787 branch-misses # 0.41% of all branches ( +- 0.56% ) 13.691837307 seconds time elapsed ( +- 0.24% ) ** after ** Performance counter stats for './hackbench 50 process 4000' (30 runs): 107784.479767 task-clock # 7.928 CPUs utilized ( +- 0.22% ) 2,834,781 context-switches # 0.026 M/sec ( +- 2.33% ) 93,083 CPU-migrations # 0.864 K/sec ( +- 3.45% ) 123,967 page-faults # 0.001 M/sec ( +- 0.15% ) 398,781,421,836 cycles # 3.700 GHz ( +- 0.22% ) stalled-cycles-frontend stalled-cycles-backend 250,189,160,419 instructions # 0.63 insns per cycle ( +- 0.09% ) 45,855,370,128 branches # 425.436 M/sec ( +- 0.10% ) 169,881,248 branch-misses # 0.37% of all branches ( +- 0.43% ) 13.596272341 seconds time elapsed ( +- 0.22% ) No regression is found, but rather we can see slightly better result. Acked-by: Christoph Lameter Signed-off-by: Joonsoo Kim Signed-off-by: Pekka Enberg