On Fri, Jun 24, 2011 at 01:57:54PM +0800, Shaohua Li wrote: > On Thu, 2011-06-23 at 14:36 +0800, Andrea Righi wrote: > > There were some reported problems in the past about trashing page cache > > when a backup software (i.e., rsync) touches a huge amount of pages (see > > for example [1]). > > > > This problem has been almost fixed by the Minchan Kim's patch [2] and a > > proper use of fadvise() in the backup software. For example this patch > > set [3] has been proposed for inclusion in rsync. > > > > However, there can be still other similar trashing problems: when the > > backup software reads all the source files, some of them may be part of > > the actual working set of the system. When a > > posix_fadvise(POSIX_FADV_DONTNEED) is performed _all_ pages are evicted > > from pagecache, both the working set and the use-once pages touched only > > by the backup software. > > > > With the following solution when posix_fadvise(POSIX_FADV_DONTNEED) is > > called for an active page instead of removing it from the page cache it > > is added to the tail of the inactive list. Otherwise, if it's already in > > the inactive list the page is removed from the page cache. > > > > In this way if the backup was the only user of a page, that page will > > be immediately removed from the page cache by calling > > posix_fadvise(POSIX_FADV_DONTNEED). If the page was also touched by > > other processes it'll be moved to the inactive list, having another > > chance of being re-added to the working set, or simply reclaimed when > > memory is needed. > > > > Testcase: > > > > - create a 1GB file called "zero" > > - run md5sum zero to read all the pages in page cache (this is to > > simulate the user activity on this file) > > - run "rsync zero zero_copy" (rsync is patched with [3]) > > - re-run md5sum zero (user activity on the working set) and measure > > the time to complete this command > > > > The test has been performed using 3.0.0-rc4 vanilla and with this patch > > applied (3.0.0-rc4-fadvise). > > > > Results: > > avg elapsed time block:block_bio_queue > > 3.0.0-rc4 4.127s 8,214 > > 3.0.0-rc4-fadvise 2.146s 0 > > > > In the first case the file is evicted from page cache completely and we > > must re-read it from the disk. In the second case the file is still in > > page cache (in the inactive list) and we don't need any other additional > > I/O operation. > > > > [1] http://marc.info/?l=rsync&m=128885034930933&w=2 > > [2] https://lkml.org/lkml/2011/2/20/57 > > [3] http://lists.samba.org/archive/rsync/2010-November/025827.html > > > > ChangeLog v1 -> v2: > > - fix comment in invalidate_mapping_pages() > > > > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > Signed-off-by: Andrea Righi <andrea@xxxxxxxxxxxxxxx> > > --- > > mm/swap.c | 9 +++++---- > > mm/truncate.c | 10 +++++++--- > > 2 files changed, 12 insertions(+), 7 deletions(-) > > > > diff --git a/mm/swap.c b/mm/swap.c > > index 3a442f1..fc8bb76 100644 > > --- a/mm/swap.c > > +++ b/mm/swap.c > > @@ -411,10 +411,11 @@ void add_page_to_unevictable_list(struct page *page) > > * > > * 1. active, mapped page -> none > > * 2. active, dirty/writeback page -> inactive, head, PG_reclaim > > - * 3. inactive, mapped page -> none > > - * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim > > - * 5. inactive, clean -> inactive, tail > > - * 6. Others -> none > > + * 3. active, clean -> inactive, tail > > + * 4. inactive, mapped page -> none > > + * 5. inactive, dirty/writeback page -> inactive, head, PG_reclaim > > + * 6. inactive, clean -> inactive, tail > > + * 7. Others -> none > > * > > * In 4, why it moves inactive's head, the VM expects the page would > > * be write it out by flusher threads as this is much more effective > > diff --git a/mm/truncate.c b/mm/truncate.c > > index 3a29a61..a36af48 100644 > > --- a/mm/truncate.c > > +++ b/mm/truncate.c > > @@ -357,11 +357,15 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping, > > if (lock_failed) > > continue; > > > > - ret = invalidate_inode_page(page); > > + if (PageActive(page)) > > + ret = 0; > > + else > > + ret = invalidate_inode_page(page); > > unlock_page(page); > > /* > > - * Invalidation is a hint that the page is no longer > > - * of interest and try to speed up its reclaim. > > + * Invalidation of an inactive page is a hint that the > > + * page is no longer of interest and try to speed up > > + * its reclaim. > > */ > > if (!ret) > > deactivate_page(page); > this looks changed behavior, active page will not be invalidated. > invalidate_mapping_pages is not just used by fadvise. for > example, /proc/sys/vm/drop_cache can't drop active pages any more with > the patch in the first invoke. Please audit other use cases too. Yes, changing the invalidate_mapping_pages() behavior completely is not good. With drop_cache we may want to actually drop the pages. I was considering to implement the Pádraig's suggestion, so do not change the current invalidate_mapping_pages() behavior and use POSIX_FADV_NOREUSE to implement the "reduce cache eligibility" logic. I'll post a new patch soon. Thanks, -Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>