Hi Jaegeuk, Sorry for the delay. I'm traveling these days.. On Wed, Nov 21, 2012 at 05:42:33PM +0800, Jaegeuk Hanse wrote: > On 11/21/2012 05:02 PM, Fengguang Wu wrote: > >On Wed, Nov 21, 2012 at 04:34:40PM +0800, Jaegeuk Hanse wrote: > >>Cc Fengguang Wu. > >> > >>On 11/21/2012 04:13 PM, metin d wrote: > >>>> Curious. Added linux-mm list to CC to catch more attention. If you run > >>>>echo 1 >/proc/sys/vm/drop_caches does it evict data-1 pages from memory? > >>>I'm guessing it'd evict the entries, but am wondering if we could run any more diagnostics before trying this. > >>> > >>>We regularly use a setup where we have two databases; one gets used frequently and the other one about once a month. It seems like the memory manager keeps unused pages in memory at the expense of frequently used database's performance. > >>>My understanding was that under memory pressure from heavily > >>>accessed pages, unused pages would eventually get evicted. Is there > >>>anything else we can try on this host to understand why this is > >>>happening? > >We may debug it this way. > > > >1) run 'fadvise data-2 0 0 dontneed' to drop data-2 cached pages > > (please double check via /proc/vmstat whether it does the expected work) > > > >2) run 'page-types -r' with root, to view the page status for the > > remaining pages of data-1 > > > >The fadvise tool comes from Andrew Morton's ext3-tools. (source code attached) > >Please compile them with options "-Dlinux -I. -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE" > > > >page-types can be found in the kernel source tree tools/vm/page-types.c > > > >Sorry that sounds a bit twisted.. I do have a patch to directly dump > >page cache status of a user specified file, however it's not > >upstreamed yet. > > Hi Fengguang, > > Thanks for you detail steps, I think metin can have a try. > > flags page-count MB symbolic-flags long-symbolic-flags > 0x0000000000000000 607699 2373 > ___________________________________ > 0x0000000100000000 343227 1340 > _______________________r___________ reserved We don't need to care about the above two pages states actually. Page cache pages will never be in the special reserved or all-flags-cleared state. > But I have some questions of the print of page-type: > > Is 2373MB here mean total memory in used include page cache? I don't > think so. > Which kind of pages will be marked reserved? > Which line of long-symbolic-flags is for page cache? The (lru && !anonymous) pages are page cache pages. Thanks, Fengguang > >>>On Tue 20-11-12 09:42:42, metin d wrote: > >>>>I have two PostgreSQL databases named data-1 and data-2 that sit on the > >>>>same machine. Both databases keep 40 GB of data, and the total memory > >>>>available on the machine is 68GB. > >>>> > >>>>I started data-1 and data-2, and ran several queries to go over all their > >>>>data. Then, I shut down data-1 and kept issuing queries against data-2. > >>>>For some reason, the OS still holds on to large parts of data-1's pages > >>>>in its page cache, and reserves about 35 GB of RAM to data-2's files. As > >>>>a result, my queries on data-2 keep hitting disk. > >>>> > >>>>I'm checking page cache usage with fincore. When I run a table scan query > >>>>against data-2, I see that data-2's pages get evicted and put back into > >>>>the cache in a round-robin manner. Nothing happens to data-1's pages, > >>>>although they haven't been touched for days. > >>>> > >>>>Does anybody know why data-1's pages aren't evicted from the page cache? > >>>>I'm open to all kind of suggestions you think it might relate to problem. > >>> Curious. Added linux-mm list to CC to catch more attention. If you run > >>>echo 1 >/proc/sys/vm/drop_caches > >>> does it evict data-1 pages from memory? > >>> > >>>>This is an EC2 m2.4xlarge instance on Amazon with 68 GB of RAM and no > >>>>swap space. The kernel version is: > >>>> > >>>>$ uname -r > >>>>3.2.28-45.62.amzn1.x86_64 > >>>>Edit: > >>>> > >>>>and it seems that I use one NUMA instance, if you think that it can a problem. > >>>> > >>>>$ numactl --hardware > >>>>available: 1 nodes (0) > >>>>node 0 cpus: 0 1 2 3 4 5 6 7 > >>>>node 0 size: 70007 MB > >>>>node 0 free: 360 MB > >>>>node distances: > >>>>node 0 > >>>> 0: 10 -- 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>