On Fri 15-02-13 17:14:10, Rob van der Heij wrote: > On 15 February 2013 12:04, Michal Hocko <mhocko@xxxxxxx> wrote: > > On Thu 14-02-13 12:39:26, Andrew Morton wrote: > >> On Thu, 14 Feb 2013 12:03:49 +0000 > >> Mel Gorman <mgorman@xxxxxxx> 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. > >> > >> 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? > > > > The script would be as simple as: > > cgcreate -g memory:backups/`whoami` > > cgset -r memory.limit_in_bytes=200MB backups/`whoami` > > cgexec -g memory:backups/`whoami` /my/backup/program > > > > It just expects that admin sets up backups group which allows the user > > to create a subgroup (w permission on the directory) and probably set up > > some reasonable cap for all backups > > Cool. This is promising enough to bridge my skills gap. It appears to > work as promised, but I would have to understand why it takes > significantly more CPU than my ugly posix_fadvise() call on close... I would guess that a lot of reclaim would be an answer. Note that each memcg has its own LRU and the limit is neforced by the per group reclaim. I wouldn't expect the difference to be very big, though. What do you mean by significantly more? -- Michal Hocko SUSE Labs -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>