kernel/git/stable/linux.git/mm/rmap.c, branch linux-2.6.21.y

mm: kill validate_anon_vma to avoid mapcount BUG

2007-08-04T16:10:25+00:00

validate_anon_vma gave a useful check on the integrity of the anon_vma list when Andrea was developing obj rmap; but it was not enabled in SLES9 itself, nor in mainline, until Nick changed commented-out RMAP_DEBUG to configurable CONFIG_DEBUG_VM in 2.6.17. Now Petr Vandrovec reports that its BUG_ON(mapcount > 100000) can easily crash a CONFIG_DEBUG_VM=y system. That limit was just an arbitrary number to protect against an infinite loop. We could raise it to something enormous (depending on sizeof struct vma and size of memory?); but I rather think validate_anon_vma has outlived its usefulness, and is better just removed - which gives a magnificent performance boost to anything like Petr's test program ;) Of course, a very long anon_vma list is bad news for preemption latency, and I believe there has been one recent report of such: let's not forget that, but validate_anon_vma only makes it worse not better. Signed-off-by: Hugh Dickins Cc: Petr Vandrovec Acked-by: Nick Piggin Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Chris Wright Signed-off-by: Greg Kroah-Hartman

[S390] page_mkclean data corruption.

2007-04-04T12:37:39+00:00

The git commit c2fda5fed81eea077363b285b66eafce20dfd45a which added the page_test_and_clear_dirty call to page_mkclean and the git commit 7658cc289288b8ae7dd2c2224549a048431222b3 which fixes the "nasty and subtle race in shared mmap'ed page writeback" problem in clear_page_dirty_for_io cause data corruption on s390. The effect of the two changes is that for every call to clear_page_dirty_for_io a page_test_and_clear_dirty is done. If the per page dirty bit is set set_page_dirty is called. Strangly clear_page_dirty_for_io is called for not-uptodate pages, e.g. over this call-chain: [<000000000007c0f2>] clear_page_dirty_for_io+0x12a/0x130 [<000000000007c494>] generic_writepages+0x258/0x3e0 [<000000000007c692>] do_writepages+0x76/0x7c [<00000000000c7a26>] __writeback_single_inode+0xba/0x3e4 [<00000000000c831a>] sync_sb_inodes+0x23e/0x398 [<00000000000c8802>] writeback_inodes+0x12e/0x140 [<000000000007b9ee>] wb_kupdate+0xd2/0x178 [<000000000007cca2>] pdflush+0x162/0x23c The bad news now is that page_test_and_clear_dirty might claim that a not-uptodate page is dirty since SetPageUptodate which resets the per page dirty bit has not yet been called. The page writeback that follows clobbers the data on disk. The simplest solution to this problem is to move the call to page_test_and_clear_dirty under the "if (page_mapped(page))". If a file backed page is mapped it is uptodate. Signed-off-by: Martin Schwidefsky

[PATCH] adapt page_lock_anon_vma() to PREEMPT_RCU

2007-03-01T22:53:39+00:00

page_lock_anon_vma() uses spin_lock() to block RCU. This doesn't work with PREEMPT_RCU, we have to do rcu_read_lock() explicitely. Otherwise, it is theoretically possible that slab returns anon_vma's memory to the system before we do spin_unlock(&anon_vma->lock). [ Hugh points out that this only matters for PREEMPT_RCU, which isn't merged yet, and may never be. Regardless, this patch is conceptually the right thing to do, even if it doesn't matter at this point. - Linus ] Signed-off-by: Oleg Nesterov Cc: Paul McKenney Cc: Nick Piggin Cc: Christoph Lameter Acked-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] page_mkclean_one(): fix call to set_pte_at()

2006-12-30T18:56:42+00:00

(akpm: macros are wonderful) Signed-off-by: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] Fix up page_mkclean_one(): virtual caches, s390

2006-12-22T18:39:35+00:00

- add flush_cache_page() for all those virtual indexed cache architectures. - handle s390. Signed-off-by: Peter Zijlstra Signed-off-by: Linus Torvalds

[PATCH] mm: more rmap debugging

2006-12-22T16:55:49+00:00

Add more debugging in the rmap code in an attempt to locate to source of the occasional "mapcount went negative" assertions. Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] mm: more commenting on lock ordering

2006-10-20T17:26:44+00:00

Clarify lockorder comments now that sys_msync dropps mmap_sem before calling do_fsync. Signed-off-by: Nick Piggin Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] move rmap BUG_ON outside DEBUG_VM

2006-10-11T18:14:19+00:00

We have a persistent dribble of reports of this BUG triggering. Its extended diagnostics were recently made conditional on CONFIG_DEBUG_VM, which was a bad idea - we want to know about it. Signed-off-by: Dave Jones Cc: Nick Piggin Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] mm: tracking shared dirty pages

2006-09-26T15:48:44+00:00

Tracking of dirty pages in shared writeable mmap()s. The idea is simple: write protect clean shared writeable pages, catch the write-fault, make writeable and set dirty. On page write-back clean all the PTE dirty bits and write protect them once again. The implementation is a tad harder, mainly because the default backing_dev_info capabilities were too loosely maintained. Hence it is not enough to test the backing_dev_info for cap_account_dirty. The current heuristic is as follows, a VMA is eligible when: - its shared writeable (vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED) - it is not a 'special' mapping (vm_flags & (VM_PFNMAP|VM_INSERTPAGE)) == 0 - the backing_dev_info is cap_account_dirty mapping_cap_account_dirty(vma->vm_file->f_mapping) - f_op->mmap() didn't change the default page protection Page from remap_pfn_range() are explicitly excluded because their COW semantics are already horrid enough (see vm_normal_page() in do_wp_page()) and because they don't have a backing store anyway. mprotect() is taught about the new behaviour as well. However it overrides the last condition. Cleaning the pages on write-back is done with page_mkclean() a new rmap call. It can be called on any page, but is currently only implemented for mapped pages, if the page is found the be of a VMA that accounts dirty pages it will also wrprotect the PTE. Finally, in fs/buffers.c:try_to_free_buffers(); remove clear_page_dirty() from under ->private_lock. This seems to be safe, since ->private_lock is used to serialize access to the buffers, not the page itself. This is needed because clear_page_dirty() will call into page_mkclean() and would thereby violate locking order. [dhowells@redhat.com: Provide a page_mkclean() implementation for NOMMU] Signed-off-by: Peter Zijlstra Cc: Hugh Dickins Signed-off-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] zoned vm counters: split NR_ANON_PAGES off from NR_FILE_MAPPED

2006-06-30T18:25:35+00:00

The current NR_FILE_MAPPED is used by zone reclaim and the dirty load calculation as the number of mapped pagecache pages. However, that is not true. NR_FILE_MAPPED includes the mapped anonymous pages. This patch separates those and therefore allows an accurate tracking of the anonymous pages per zone. It then becomes possible to determine the number of unmapped pages per zone and we can avoid scanning for unmapped pages if there are none. Also it may now be possible to determine the mapped/unmapped ratio in get_dirty_limit. Isnt the number of anonymous pages irrelevant in that calculation? Note that this will change the meaning of the number of mapped pages reported in /proc/vmstat /proc/meminfo and in the per node statistics. This may affect user space tools that monitor these counters! NR_FILE_MAPPED works like NR_FILE_DIRTY. It is only valid for pagecache pages. Signed-off-by: Christoph Lameter Cc: Trond Myklebust Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds