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authorKen Chen <kenchen@google.com>2007-02-10 01:43:15 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-02-11 10:51:19 -0800
commit767193253bbac889e176f90b6f17b7015f986551 (patch)
treea81c5c90d14c7892e6d7adb0432f4dff4ca3f906 /fs/ramfs
parentbd8029b66069d29fd02c304599411ca9bb7fa38c (diff)
downloadop-kernel-dev-767193253bbac889e176f90b6f17b7015f986551.zip
op-kernel-dev-767193253bbac889e176f90b6f17b7015f986551.tar.gz
[PATCH] simplify shmem_aops.set_page_dirty() method
shmem backed file does not have page writeback, nor it participates in backing device's dirty or writeback accounting. So using generic __set_page_dirty_nobuffers() for its .set_page_dirty aops method is a bit overkill. It unnecessarily prolongs shm unmap latency. For example, on a densely populated large shm segment (sevearl GBs), the unmapping operation becomes painfully long. Because at unmap, kernel transfers dirty bit in PTE into page struct and to the radix tree tag. The operation of tagging the radix tree is particularly expensive because it has to traverse the tree from the root to the leaf node on every dirty page. What's bothering is that radix tree tag is used for page write back. However, shmem is memory backed and there is no page write back for such file system. And in the end, we spend all that time tagging radix tree and none of that fancy tagging will be used. So let's simplify it by introduce a new aops __set_page_dirty_no_writeback and this will speed up shm unmap. Signed-off-by: Ken Chen <kenchen@google.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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