From: Mel Gorman <mgorman@suse.de> To: Andrew Morton <akpm@linux-foundation.org> Cc: Rob van der Heij <rvdheij@gmail.com>, Hugh Dickins <hughd@google.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] mm: fadvise: Drain all pagevecs if POSIX_FADV_DONTNEED fails to discard all pages Date: Tue, 19 Feb 2013 11:57:30 +0000 [thread overview] Message-ID: <20130219115729.GS4365@suse.de> (raw) In-Reply-To: <20130214123926.599fcef8.akpm@linux-foundation.org> On Thu, Feb 14, 2013 at 12:39:26PM -0800, Andrew Morton wrote: > On Thu, 14 Feb 2013 12:03:49 +0000 > Mel Gorman <mgorman@suse.de> wrote: > > > Rob van der Heij reported the following (paraphrased) on private mail. > > > > The scenario is that I want to avoid backups to fill up the page > > cache and purge stuff that is more likely to be used again (this is > > with s390x Linux on z/VM, so I don't give it as much memory that > > we don't care anymore). So I have something with LD_PRELOAD that > > intercepts the close() call (from tar, in this case) and issues > > a posix_fadvise() just before closing the file. > > > > This mostly works, except for small files (less than 14 pages) > > that remains in page cache after the face. > > Sigh. We've had the "my backups swamp pagecache" thing for 15 years > and it's still happening. > Yes. There have been variations of it too such as applications being pushed prematurely into swap. I'm not certain how well we currently handle that because I haven't checked in a few months. > It should be possible nowadays to toss your backup application into a > container to constrain its pagecache usage. So we can type > > run-in-a-memcg -m 200MB /my/backup/program > > and voila. Does such a script exist and work? > Michal already gave an example. It might work slower if the backup application has to stall in direct reclaim to keep the container within limits though. > > --- a/mm/fadvise.c > > +++ b/mm/fadvise.c > > @@ -17,6 +17,7 @@ > > #include <linux/fadvise.h> > > #include <linux/writeback.h> > > #include <linux/syscalls.h> > > +#include <linux/swap.h> > > > > #include <asm/unistd.h> > > > > @@ -120,9 +121,22 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) > > start_index = (offset+(PAGE_CACHE_SIZE-1)) >> PAGE_CACHE_SHIFT; > > end_index = (endbyte >> PAGE_CACHE_SHIFT); > > > > - if (end_index >= start_index) > > - invalidate_mapping_pages(mapping, start_index, > > + if (end_index >= start_index) { > > + unsigned long count = invalidate_mapping_pages(mapping, > > + start_index, end_index); > > + > > + /* > > + * If fewer pages were invalidated than expected then > > + * it is possible that some of the pages were on > > + * a per-cpu pagevec for a remote CPU. Drain all > > + * pagevecs and try again. > > + */ > > + if (count < (end_index - start_index + 1)) { > > + lru_add_drain_all(); > > + invalidate_mapping_pages(mapping, start_index, > > end_index); > > + } > > + } > > break; > > default: > > ret = -EINVAL; > > Those LRU pagevecs are a right pain. They provided useful gains way > back when I first inflicted them upon Linux, but it would be nice to > confirm whether they're still worthwhile and if so, whether the > benefits can be replicated with some less intrusive scheme. > I know. Unfortunately I've had "Implement pagevec removal and test" on my TODO list for the guts of a year now. It's long overdue to actually sit down and just do it. It's a similar story for the per-cpu lists in front of the page allocator which are overdue to see if they can be replaced. I actually have a prototype replacement for that lying around but it performed slower in tests and has bit-rotted since but it ran slower and has bit-rotted since as it was based on kernel 3.4. -- Mel Gorman SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@suse.de> To: Andrew Morton <akpm@linux-foundation.org> Cc: Rob van der Heij <rvdheij@gmail.com>, Hugh Dickins <hughd@google.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] mm: fadvise: Drain all pagevecs if POSIX_FADV_DONTNEED fails to discard all pages Date: Tue, 19 Feb 2013 11:57:30 +0000 [thread overview] Message-ID: <20130219115729.GS4365@suse.de> (raw) In-Reply-To: <20130214123926.599fcef8.akpm@linux-foundation.org> On Thu, Feb 14, 2013 at 12:39:26PM -0800, Andrew Morton wrote: > On Thu, 14 Feb 2013 12:03:49 +0000 > Mel Gorman <mgorman@suse.de> wrote: > > > Rob van der Heij reported the following (paraphrased) on private mail. > > > > The scenario is that I want to avoid backups to fill up the page > > cache and purge stuff that is more likely to be used again (this is > > with s390x Linux on z/VM, so I don't give it as much memory that > > we don't care anymore). So I have something with LD_PRELOAD that > > intercepts the close() call (from tar, in this case) and issues > > a posix_fadvise() just before closing the file. > > > > This mostly works, except for small files (less than 14 pages) > > that remains in page cache after the face. > > Sigh. We've had the "my backups swamp pagecache" thing for 15 years > and it's still happening. > Yes. There have been variations of it too such as applications being pushed prematurely into swap. I'm not certain how well we currently handle that because I haven't checked in a few months. > It should be possible nowadays to toss your backup application into a > container to constrain its pagecache usage. So we can type > > run-in-a-memcg -m 200MB /my/backup/program > > and voila. Does such a script exist and work? > Michal already gave an example. It might work slower if the backup application has to stall in direct reclaim to keep the container within limits though. > > --- a/mm/fadvise.c > > +++ b/mm/fadvise.c > > @@ -17,6 +17,7 @@ > > #include <linux/fadvise.h> > > #include <linux/writeback.h> > > #include <linux/syscalls.h> > > +#include <linux/swap.h> > > > > #include <asm/unistd.h> > > > > @@ -120,9 +121,22 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) > > start_index = (offset+(PAGE_CACHE_SIZE-1)) >> PAGE_CACHE_SHIFT; > > end_index = (endbyte >> PAGE_CACHE_SHIFT); > > > > - if (end_index >= start_index) > > - invalidate_mapping_pages(mapping, start_index, > > + if (end_index >= start_index) { > > + unsigned long count = invalidate_mapping_pages(mapping, > > + start_index, end_index); > > + > > + /* > > + * If fewer pages were invalidated than expected then > > + * it is possible that some of the pages were on > > + * a per-cpu pagevec for a remote CPU. Drain all > > + * pagevecs and try again. > > + */ > > + if (count < (end_index - start_index + 1)) { > > + lru_add_drain_all(); > > + invalidate_mapping_pages(mapping, start_index, > > end_index); > > + } > > + } > > break; > > default: > > ret = -EINVAL; > > Those LRU pagevecs are a right pain. They provided useful gains way > back when I first inflicted them upon Linux, but it would be nice to > confirm whether they're still worthwhile and if so, whether the > benefits can be replicated with some less intrusive scheme. > I know. Unfortunately I've had "Implement pagevec removal and test" on my TODO list for the guts of a year now. It's long overdue to actually sit down and just do it. It's a similar story for the per-cpu lists in front of the page allocator which are overdue to see if they can be replaced. I actually have a prototype replacement for that lying around but it performed slower in tests and has bit-rotted since but it ran slower and has bit-rotted since as it was based on kernel 3.4. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2013-02-19 11:57 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-02-14 12:03 [PATCH] mm: fadvise: Drain all pagevecs if POSIX_FADV_DONTNEED fails to discard all pages Mel Gorman 2013-02-14 12:03 ` Mel Gorman 2013-02-14 17:07 ` Rob van der Heij 2013-02-14 17:07 ` Rob van der Heij 2013-02-14 20:39 ` Andrew Morton 2013-02-14 20:39 ` Andrew Morton 2013-02-15 11:04 ` Michal Hocko 2013-02-15 11:04 ` Michal Hocko 2013-02-15 16:14 ` Rob van der Heij 2013-02-15 16:14 ` Rob van der Heij 2013-02-15 16:48 ` Michal Hocko 2013-02-15 16:48 ` Michal Hocko 2013-02-19 11:57 ` Mel Gorman [this message] 2013-02-19 11:57 ` Mel Gorman
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