On Fri, Jun 24, 2011 at 07:06:42AM +0900, Minchan Kim wrote: > Hi Andrea, > Sorry for late response. > These day, I have no time to see the LKML. > > On Thu, Jun 23, 2011 at 3:36 PM, Andrea Righi <andrea@xxxxxxxxxxxxxxx> 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. > > Agreed. It's rather aggressive. > > > > > 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 > > > > Great! > > > 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 > > Nitpick. > I would like to put together them by on line as rather than adding another line. > 5, [in]active, clean-> inactive, tail. > I guess it's more easy to understand. Agreed. > > If you want to put it in another line, please change below comment, too. > "In 5, why it moves inactive's head.." Oh right. I'd put both on a single line anyway, as you suggested. > > > * > > * 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); > > I would like to add comment. > "Invalidation of active page is rather aggressive as we can't make > sure it's not a working set of other processes. > deactivate_page would move it into inactive's tail so the page will > have a chance to activate again if other processes > touch it. otherwise, it would be reclaimed simply". OK. > > > + if (PageActive(page)) > > + ret = 0; > > + else > > + ret = invalidate_inode_page(page); > > > You have to change description of invalidate_mapping_pages. > > * invalidate_mapping_pages() will not block on IO activity. It will not > * invalidate pages which are dirty, locked, under writeback, mapped into > * pagetables or on active lru. Correct. > > > 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); > > -- > > 1.7.4.1 > > > > > > Otherwise, Looks good to me. > > Acked-by: Minchan Kim <minchan.kim@xxxxxxxxx> > > -- > Kind regards, > Minchan Kim Thanks for the review. I'll add all your comments and post a new version. -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>