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DateTue, 15 Jan 2008 23:55:17 +0100
From"Daniel_Spång" <>
SubjectRe: [RFC][PATCH 4/5] memory_pressure_notify() caller
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Hi,

On 1/15/08, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
the notification point to happen whenever the VM moves an anonymous page to the inactive list - this is a pretty good indication that there are unused anonymous pages present which will be very likely swapped out soon.

+ /* deal with the case where there is no + * swap but an anonymous page would be + * moved to the inactive list. + */
+ if (!total_swap_pages && reclaim_mapped && + PageAnon(page)) + inactivated_anon = 1;

As you know I have had some concerns regarding a too early notification in a swapless system.

I did a test with a populated page cache in a swapless system:
$ cat /bigfile > /dev/null # populate page cache
$ cat /proc/meminfo
MemTotal:      1037040 kB
MemFree:        113976 kB
Buffers:          1068 kB
Cached:         907552 kB
SwapCached:          0 kB
Active:          11116 kB
Inactive:       903968 kB
HighTotal:      130992 kB
HighFree:          252 kB
LowTotal:       906048 kB
LowFree:        113724 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:              36 kB
Writeback:           0 kB
AnonPages:        6484 kB
Mapped:           1216 kB
Slab:             4024 kB
SReclaimable:      864 kB
SUnreclaim:       3160 kB
PageTables:        444 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:    518520 kB
Committed_AS:    18816 kB
VmallocTotal:   114680 kB
VmallocUsed:       904 kB
VmallocChunk:   113672 kB
Start to allocate memory, 10 MB every second, exit on notification.
$ cat /proc/meminfo # just after notification
MemTotal: 1037040 kB
MemFree: 123468 kB
Buffers: 876 kB
Cached: 897976 kB
SwapCached: 0 kB
Active: 12984 kB
Inactive: 892332 kB
HighTotal: 130992 kB
HighFree: 1064 kB
LowTotal: 906048 kB
LowFree: 122404 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 6484 kB
Mapped: 1220 kB
Slab: 4012 kB
SReclaimable: 864 kB
SUnreclaim: 3148 kB
PageTables: 448 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 518520 kB
Committed_AS: 18816 kB
VmallocTotal: 114680 kB
VmallocUsed: 904 kB
VmallocChunk: 113672 kB

The notification fires after only ~100 MB allocated, i.e., when page reclaim is beginning to nag from page cache. Isn't this a bit early? Repeating the test with swap enabled results in a notification after ~600 MB allocated, which is more reasonable and just before the system starts to swap.

Cheers,
Daniel



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