Re: Problem in Page Cache Replacement

metin d
2012-11-21T10:00:31Z

[-- Attachment #1: Type: text/plain, Size: 4684 bytes --]

Hi Fengguang,

I run tests and attached the results. The line below I guess shows the data-1 page caches.

0x000000080000006c       6584051    25718  __RU_lA___________________P________    referenced,uptodate,lru,active,private
Metin

________________________________
From: Jaegeuk Hanse <jaegeuk.hanse@gmail.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: metin d <metdos@yahoo.com>; Jan Kara <jack@suse.cz>; "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>; "linux-mm@kvack.org" <linux-mm@kvack.org>
Sent: Wednesday, November 21, 2012 11:42 AM
Subject: Re: Problem in Page Cache Replacement

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

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?

Regards,
Jaegeuk

>
> 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

[-- Attachment #2: page-types_after.txt --]
[-- Type: text/plain, Size: 5453 bytes --]

flags page-count MB symbolic-flags long-symbolic-flags
0x0000000000000000 5508317 21516 ___________________________________
0x0000000100000000 335993 1312 _______________________r___________ reserved
0x0000002100000000 35634 139 _______________________r____O______ reserved,owner_private
0x0000000000010000 45069 176 ________________T__________________ compound_tail
0x0000002000000000 1516 5 ____________________________O______ owner_private
0x0000000800000004 1 0 __R_______________________P________ referenced,private
0x0000000000008000 10 0 _______________H___________________ compound_head
0x0000000000000004 1 0 __R________________________________ referenced
0x0000000800000024 166 0 __R__l____________________P________ referenced,lru,private
0x0000000400000028 295 1 ___U_l___________________d_________ uptodate,lru,mappedtodisk
0x0001000400000028 3 0 ___U_l___________________d_____I___ uptodate,lru,mappedtodisk,readahead
0x0000000000000028 1 0 ___U_l_____________________________ uptodate,lru
0x000000040000002c 262144 1024 __RU_l___________________d_________ referenced,uptodate,lru,mappedtodisk
0x000000080000002c 5 0 __RU_l____________________P________ referenced,uptodate,lru,private
0x000000000000403c 185 0 __RUDl________b____________________ referenced,uptodate,dirty,lru,swapbacked
0x0000000800000060 163 0 _____lA___________________P________ lru,active,private
0x0000000800000064 36739 143 __R__lA___________________P________ referenced,lru,active,private
0x0000000400000068 527810 2061 ___U_lA__________________d_________ uptodate,lru,active,mappedtodisk
0x0000000800000068 576 2 ___U_lA___________________P________ uptodate,lru,active,private
0x0000000c00000068 116 0 ___U_lA__________________dP________ uptodate,lru,active,mappedtodisk,private
0x000000080000006c 6584051 25718 __RU_lA___________________P________ referenced,uptodate,lru,active,private
0x000000040000006c 1302211 5086 __RU_lA__________________d_________ referenced,uptodate,lru,active,mappedtodisk
0x0000000c0000006c 431 1 __RU_lA__________________dP________ referenced,uptodate,lru,active,mappedtodisk,private
0x000000000000006c 128 0 __RU_lA____________________________ referenced,uptodate,lru,active
0x0000000800000074 2 0 __R_DlA___________________P________ referenced,dirty,lru,active,private
0x0000000000004078 56 0 ___UDlA_______b____________________ uptodate,dirty,lru,active,swapbacked
0x000000000000407c 122 0 __RUDlA_______b____________________ referenced,uptodate,dirty,lru,active,swapbacked
0x000000080000007c 1 0 __RUDlA___________________P________ referenced,uptodate,dirty,lru,active,private
0x0000000000008080 14495 56 _______S_______H___________________ slab,compound_head
0x0000000000000080 250498 978 _______S___________________________ slab
0x0000000000000400 2990908 11683 __________B________________________ buddy
0x0000000000000800 16 0 ___________M_______________________ mmap
0x0000000100000804 1 0 __R________M___________r___________ referenced,mmap,reserved
0x000000060004082c 391 1 __RU_l_____M______u_____md_________ referenced,uptodate,lru,mmap,unevictable,mlocked,mappedtodisk
0x0000000a0004082c 321 1 __RU_l_____M______u_____m_P________ referenced,uptodate,lru,mmap,unevictable,mlocked,private
0x0000000000004838 8450 33 ___UDl_____M__b____________________ uptodate,dirty,lru,mmap,swapbacked
0x000000000000483c 2045 7 __RUDl_____M__b____________________ referenced,uptodate,dirty,lru,mmap,swapbacked
0x0000000800000868 19 0 ___U_lA____M______________P________ uptodate,lru,active,mmap,private
0x0000000400000868 5 0 ___U_lA____M_____________d_________ uptodate,lru,active,mmap,mappedtodisk
0x000000040000086c 1891 7 __RU_lA____M_____________d_________ referenced,uptodate,lru,active,mmap,mappedtodisk
0x000000080000086c 126 0 __RU_lA____M______________P________ referenced,uptodate,lru,active,mmap,private
0x0000000000004878 85 0 ___UDlA____M__b____________________ uptodate,dirty,lru,active,mmap,swapbacked
0x000000000000487c 2263 8 __RUDlA____M__b____________________ referenced,uptodate,dirty,lru,active,mmap,swapbacked
0x0000000000005008 13 0 ___U________a_b____________________ uptodate,anonymous,swapbacked
0x0000000000005808 16 0 ___U_______Ma_b____________________ uptodate,mmap,anonymous,swapbacked
0x0000000200045828 8 0 ___U_l_____Ma_b___u_____m__________ uptodate,lru,mmap,anonymous,swapbacked,unevictable,mlocked
0x000000020004582c 651 2 __RU_l_____Ma_b___u_____m__________ referenced,uptodate,lru,mmap,anonymous,swapbacked,unevictable,mlocked
0x0000000000005868 8058 31 ___U_lA____Ma_b____________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c 42 0 __RU_lA____Ma_b____________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
total 17922048 70008

[-- Attachment #3: page-types_before.txt --]
[-- Type: text/plain, Size: 5551 bytes --]

flags page-count MB symbolic-flags long-symbolic-flags
0x0000000000000000 121628 475 ___________________________________
0x0000000100000000 335993 1312 _______________________r___________ reserved
0x0000002100000000 35634 139 _______________________r____O______ reserved,owner_private
0x0000000000010000 45429 177 ________________T__________________ compound_tail
0x0000002000000000 1389 5 ____________________________O______ owner_private
0x0000000400000001 6 0 L________________________d_________ locked,mappedtodisk
0x0000000000008000 10 0 _______________H___________________ compound_head
0x0000000000000004 1 0 __R________________________________ referenced
0x0000000400000021 64 0 L____l___________________d_________ locked,lru,mappedtodisk
0x0001000400000021 1 0 L____l___________________d_____I___ locked,lru,mappedtodisk,readahead
0x0000000800000024 171 0 __R__l____________________P________ referenced,lru,private
0x0000000400000028 4093 15 ___U_l___________________d_________ uptodate,lru,mappedtodisk
0x0001000400000028 59 0 ___U_l___________________d_____I___ uptodate,lru,mappedtodisk,readahead
0x0000000000000028 1 0 ___U_l_____________________________ uptodate,lru
0x000000040000002c 8598032 33586 __RU_l___________________d_________ referenced,uptodate,lru,mappedtodisk
0x000000080000002c 10 0 __RU_l____________________P________ referenced,uptodate,lru,private
0x000000000000403c 185 0 __RUDl________b____________________ referenced,uptodate,dirty,lru,swapbacked
0x0000000800000060 163 0 _____lA___________________P________ lru,active,private
0x0000000800000064 36741 143 __R__lA___________________P________ referenced,lru,active,private
0x0000000400000068 527834 2061 ___U_lA__________________d_________ uptodate,lru,active,mappedtodisk
0x0000000800000068 695 2 ___U_lA___________________P________ uptodate,lru,active,private
0x0000000c00000068 116 0 ___U_lA__________________dP________ uptodate,lru,active,mappedtodisk,private
0x000000080000006c 6584066 25719 __RU_lA___________________P________ referenced,uptodate,lru,active,private
0x000000040000006c 1325273 5176 __RU_lA__________________d_________ referenced,uptodate,lru,active,mappedtodisk
0x0000000c0000006c 431 1 __RU_lA__________________dP________ referenced,uptodate,lru,active,mappedtodisk,private
0x000000000000006c 128 0 __RU_lA____________________________ referenced,uptodate,lru,active
0x0000000000004078 56 0 ___UDlA_______b____________________ uptodate,dirty,lru,active,swapbacked
0x000000000000407c 122 0 __RUDlA_______b____________________ referenced,uptodate,dirty,lru,active,swapbacked
0x000000080000007c 1 0 __RUDlA___________________P________ referenced,uptodate,dirty,lru,active,private
0x0000000000008080 14571 56 _______S_______H___________________ slab,compound_head
0x0000000000000080 250546 978 _______S___________________________ slab
0x0000000000000400 14701 57 __________B________________________ buddy
0x0000000000000800 16 0 ___________M_______________________ mmap
0x0000000100000804 1 0 __R________M___________r___________ referenced,mmap,reserved
0x000000060004082c 391 1 __RU_l_____M______u_____md_________ referenced,uptodate,lru,mmap,unevictable,mlocked,mappedtodisk
0x0000000a0004082c 321 1 __RU_l_____M______u_____m_P________ referenced,uptodate,lru,mmap,unevictable,mlocked,private
0x0000000000004838 8385 32 ___UDl_____M__b____________________ uptodate,dirty,lru,mmap,swapbacked
0x000000000000483c 2045 7 __RUDl_____M__b____________________ referenced,uptodate,dirty,lru,mmap,swapbacked
0x0000000800000868 19 0 ___U_lA____M______________P________ uptodate,lru,active,mmap,private
0x0000000400000868 5 0 ___U_lA____M_____________d_________ uptodate,lru,active,mmap,mappedtodisk
0x000000040000086c 1891 7 __RU_lA____M_____________d_________ referenced,uptodate,lru,active,mmap,mappedtodisk
0x000000080000086c 126 0 __RU_lA____M______________P________ referenced,uptodate,lru,active,mmap,private
0x0000000000004878 85 0 ___UDlA____M__b____________________ uptodate,dirty,lru,active,mmap,swapbacked
0x000000000000487c 2263 8 __RUDlA____M__b____________________ referenced,uptodate,dirty,lru,active,mmap,swapbacked
0x0000000000005008 4 0 ___U________a_b____________________ uptodate,anonymous,swapbacked
0x0000000000005808 25 0 ___U_______Ma_b____________________ uptodate,mmap,anonymous,swapbacked
0x0000000200045828 8 0 ___U_l_____Ma_b___u_____m__________ uptodate,lru,mmap,anonymous,swapbacked,unevictable,mlocked
0x000000020004582c 651 2 __RU_l_____Ma_b___u_____m__________ referenced,uptodate,lru,mmap,anonymous,swapbacked,unevictable,mlocked
0x0000000000005868 7623 29 ___U_lA____Ma_b____________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c 39 0 __RU_lA____Ma_b____________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
total 17922048 70008