user/sven/linux.git/include/linux/page-flags.h, branch v3.10.44

s390/mm: implement software dirty bits

2013-02-14T14:55:23Z

The s390 architecture is unique in respect to dirty page detection, it uses the change bit in the per-page storage key to track page modifications. All other architectures track dirty bits by means of page table entries. This property of s390 has caused numerous problems in the past, e.g. see git commit ef5d437f71afdf4a "mm: fix XFS oops due to dirty pages without buffers on s390". To avoid future issues in regard to per-page dirty bits convert s390 to a fault based software dirty bit detection mechanism. All user page table entries which are marked as clean will be hardware read-only, even if the pte is supposed to be writable. A write by the user process will trigger a protection fault which will cause the user pte to be marked as dirty and the hardware read-only bit is removed. With this change the dirty bit in the storage key is irrelevant for Linux as a host, but the storage key is still required for KVM guests. The effect is that page_test_and_clear_dirty and the related code can be removed. The referenced bit in the storage key is still used by the page_test_and_clear_young primitive to provide page age information. For page cache pages of mappings with mapping_cap_account_dirty there will not be any change in behavior as the dirty bit tracking already uses read-only ptes to control the amount of dirty pages. Only for swap cache pages and pages of mappings without mapping_cap_account_dirty there can be additional protection faults. To avoid an excessive number of additional faults the mk_pte primitive checks for PageDirty if the pgprot value allows for writes and pre-dirties the pte. That avoids all additional faults for tmpfs and shmem pages until these pages are added to the swap cache. Signed-off-by: Martin Schwidefsky

mm: Fix PageHead when !CONFIG_PAGEFLAGS_EXTENDED

2012-12-26T22:57:34Z

Unfortunately with !CONFIG_PAGEFLAGS_EXTENDED, (!PageHead) is false, and (PageHead) is true, for tail pages. If this is indeed the intended behavior, which I doubt because it breaks cache cleaning on some ARM systems, then the nomenclature is highly problematic. This patch makes sure PageHead is only true for head pages and PageTail is only true for tail pages, and neither is true for non-compound pages. [ This buglet seems ancient - seems to have been introduced back in Apr 2008 in commit 6a1e7f777f61: "pageflags: convert to the use of new macros". And the reason nobody noticed is because the PageHead() tests are almost all about just sanity-checking, and only used on pages that are actual page heads. The fact that the old code returned true for tail pages too was thus not really noticeable. - Linus ] Signed-off-by: Christoffer Dall Acked-by: Andrea Arcangeli Cc: Andrew Morton Cc: Will Deacon Cc: Steve Capper Cc: Christoph Lameter Cc: stable@kernel.org # 2.6.26+ 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

Merge tag 'bug-for-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux

2012-03-24T17:08:39Z

Pull cleanup from Paul Gortmaker: "The changes shown here are to unify linux's BUG support under the one file. Due to historical reasons, we have some BUG code in bug.h and some in kernel.h -- i.e. the support for BUILD_BUG in linux/kernel.h predates the addition of linux/bug.h, but old code in kernel.h wasn't moved to bug.h at that time. As a band-aid, kernel.h was including to pseudo link them. This has caused confusion[1] and general yuck/WTF[2] reactions. Here is an example that violates the principle of least surprise: CC lib/string.o lib/string.c: In function 'strlcat': lib/string.c:225:2: error: implicit declaration of function 'BUILD_BUG_ON' make[2]: *** [lib/string.o] Error 1 $ $ grep linux/bug.h lib/string.c #include $ We've included for the BUG infrastructure and yet we still get a compile fail! [We've not kernel.h for BUILD_BUG_ON.] Ugh - very confusing for someone who is new to kernel development. With the above in mind, the goals of this changeset are: 1) find and fix any include/*.h files that were relying on the implicit presence of BUG code. 2) find and fix any C files that were consuming kernel.h and hence relying on implicitly getting some/all BUG code. 3) Move the BUG related code living in kernel.h to 4) remove the asm/bug.h from kernel.h to finally break the chain. During development, the order was more like 3-4, build-test, 1-2. But to ensure that git history for bisect doesn't get needless build failures introduced, the commits have been reorderd to fix the problem areas in advance. [1] https://lkml.org/lkml/2012/1/3/90 [2] https://lkml.org/lkml/2012/1/17/414" Fix up conflicts (new radeon file, reiserfs header cleanups) as per Paul and linux-next. * tag 'bug-for-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux: kernel.h: doesn't explicitly use bug.h, so don't include it. bug: consolidate BUILD_BUG_ON with other bug code BUG: headers with BUG/BUG_ON etc. need linux/bug.h bug.h: add include of it to various implicit C users lib: fix implicit users of kernel.h for TAINT_WARN spinlock: macroize assert_spin_locked to avoid bug.h dependency x86: relocate get/set debugreg fcns to include/asm/debugreg.

thp: allow a hwpoisoned head page to be put back to LRU

2012-03-22T00:54:58Z

Andrea Arcangeli pointed out to me that a check in __memory_failure() which was intended to prevent THP tail pages from being checked for the absence of the PG_lru flag (something that is always the case), was also preventing THP head pages from being checked. A THP head page could actually benefit from the call to shake_page() by ending up being put back to a LRU, provided it had been waiting in a pagevec array. Andrea suggested that the "!PageTransCompound(p)" in the if-statement should be replaced by a "!PageTransTail(p)", thus allowing THP head pages to be checked and possibly shaken. Signed-off-by: Dean Nelson Cc: Jin Dongming Reviewed-by: Andrea Arcangeli Cc: Andi Kleen Cc: Hidetoshi Seto Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

BUG: headers with BUG/BUG_ON etc. need linux/bug.h

2012-03-04T22:54:34Z

If a header file is making use of BUG, BUG_ON, BUILD_BUG_ON, or any other BUG variant in a static inline (i.e. not in a #define) then that header really should be including and not just expecting it to be implicitly present. We can make this change risk-free, since if the files using these headers didn't have exposure to linux/bug.h already, they would have been causing compile failures/warnings. Signed-off-by: Paul Gortmaker

Merge branch 'slub/lockless' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6

2011-07-30T18:21:48Z

* 'slub/lockless' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6: (21 commits) slub: When allocating a new slab also prep the first object slub: disable interrupts in cmpxchg_double_slab when falling back to pagelock Avoid duplicate _count variables in page_struct Revert "SLUB: Fix build breakage in linux/mm_types.h" SLUB: Fix build breakage in linux/mm_types.h slub: slabinfo update for cmpxchg handling slub: Not necessary to check for empty slab on load_freelist slub: fast release on full slab slub: Add statistics for the case that the current slab does not match the node slub: Get rid of the another_slab label slub: Avoid disabling interrupts in free slowpath slub: Disable interrupts in free_debug processing slub: Invert locking and avoid slab lock slub: Rework allocator fastpaths slub: Pass kmem_cache struct to lock and freeze slab slub: explicit list_lock taking slub: Add cmpxchg_double_slab() mm: Rearrange struct page slub: Move page->frozen handling near where the page->freelist handling occurs slub: Do not use frozen page flag but a bit in the page counters ...

mm: use const struct page for r/o page-flag accessor methods

2011-07-26T03:57:07Z

In a subsquent patch I have a const struct page in my hand... [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Ian Campbell Cc: Andrea Arcangeli Cc: Rik van Riel Cc: Martin Schwidefsky Cc: Michel Lespinasse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

slub: Do not use frozen page flag but a bit in the page counters

2011-07-02T10:26:52Z

Do not use a page flag for the frozen bit. It needs to be part of the state that is handled with cmpxchg_double(). So use a bit in the counter struct in the page struct for that purpose. Signed-off-by: Christoph Lameter Signed-off-by: Pekka Enberg

[S390] mm: fix storage key handling

2011-05-29T10:40:51Z

page_get_storage_key() and page_set_storage_key() expect a page address and not its page frame number. This got inconsistent with 2d42552d "[S390] merge page_test_dirty and page_clear_dirty". Result is that we read/write storage keys from random pages and do not have a working dirty bit tracking at all. E.g. SetPageUpdate() doesn't clear the dirty bit of requested pages, which for example ext4 doesn't like very much and panics after a while. Unable to handle kernel paging request at virtual user address (null) Oops: 0004 [#1] PREEMPT SMP DEBUG_PAGEALLOC Modules linked in: CPU: 1 Not tainted 2.6.39-07551-g139f37f-dirty #152 Process flush-94:0 (pid: 1576, task: 000000003eb34538, ksp: 000000003c287b70) Krnl PSW : 0704c00180000000 0000000000316b12 (jbd2_journal_file_inode+0x10e/0x138) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 EA:3 Krnl GPRS: 0000000000000000 0000000000000000 0000000000000000 0700000000000000 0000000000316a62 000000003eb34cd0 0000000000000025 000000003c287b88 0000000000000001 000000003c287a70 000000003f1ec678 000000003f1ec000 0000000000000000 000000003e66ec00 0000000000316a62 000000003c287988 Krnl Code: 0000000000316b04: f0a0000407f4 srp 4(11,%r0),2036,0 0000000000316b0a: b9020022 ltgr %r2,%r2 0000000000316b0e: a7740015 brc 7,316b38 >0000000000316b12: e3d0c0000024 stg %r13,0(%r12) 0000000000316b18: 4120c010 la %r2,16(%r12) 0000000000316b1c: 4130d060 la %r3,96(%r13) 0000000000316b20: e340d0600004 lg %r4,96(%r13) 0000000000316b26: c0e50002b567 brasl %r14,36d5f4 Call Trace: ([<0000000000316a62>] jbd2_journal_file_inode+0x5e/0x138) [<00000000002da13c>] mpage_da_map_and_submit+0x2e8/0x42c [<00000000002daac2>] ext4_da_writepages+0x2da/0x504 [<00000000002597e8>] writeback_single_inode+0xf8/0x268 [<0000000000259f06>] writeback_sb_inodes+0xd2/0x18c [<000000000025a700>] writeback_inodes_wb+0x80/0x168 [<000000000025aa92>] wb_writeback+0x2aa/0x324 [<000000000025abde>] wb_do_writeback+0xd2/0x274 [<000000000025ae3a>] bdi_writeback_thread+0xba/0x1c4 [<00000000001737be>] kthread+0xa6/0xb0 [<000000000056c1da>] kernel_thread_starter+0x6/0xc [<000000000056c1d4>] kernel_thread_starter+0x0/0xc INFO: lockdep is turned off. Last Breaking-Event-Address: [<0000000000316a8a>] jbd2_journal_file_inode+0x86/0x138 Reported-by: Sebastian Ott Signed-off-by: Heiko Carstens