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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2008-07-04 09:59:24 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-04 10:40:04 -0700 |
commit | 251b97f552b1ad414cc5a9ccc8e4e94503edd5fc (patch) | |
tree | 5d7559154edb8eb2069f39b6be99ffc2484580cd /CREDITS | |
parent | cde53535991fbb5c34a1566f25955297c1487b8d (diff) | |
download | op-kernel-dev-251b97f552b1ad414cc5a9ccc8e4e94503edd5fc.zip op-kernel-dev-251b97f552b1ad414cc5a9ccc8e4e94503edd5fc.tar.gz |
mm: dirty page accounting vs VM_MIXEDMAP
Dirty page accounting accurately measures the amound of dirty pages in
writable shared mappings by mapping the pages RO (as indicated by
vma_wants_writenotify). We then trap on first write and call
set_page_dirty() on the page, after which we map the page RW and
continue execution.
When we launder dirty pages, we call clear_page_dirty_for_io() which
clears both the dirty flag, and maps the page RO again before we start
writeout so that the story can repeat itself.
vma_wants_writenotify() excludes VM_PFNMAP on the basis that we cannot
do the regular dirty page stuff on raw PFNs and the memory isn't going
anywhere anyway.
The recently introduced VM_MIXEDMAP mixes both !pfn_valid() and
pfn_valid() pages in a single mapping.
We can't do dirty page accounting on !pfn_valid() pages as stated
above, and mapping them RO causes them to be COW'ed on write, which
breaks VM_SHARED semantics.
Excluding VM_MIXEDMAP in vma_wants_writenotify() would mean we don't do
the regular dirty page accounting for the pfn_valid() pages, which
would bring back all the head-aches from inaccurate dirty page
accounting.
So instead, we let the !pfn_valid() pages get mapped RO, but fix them
up unconditionally in the fault path.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Hugh Dickins <hugh@veritas.com>
Cc: "Jared Hulbert" <jaredeh@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'CREDITS')
0 files changed, 0 insertions, 0 deletions