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SubjectRe: tuning/tweaking VM settings for low memory (preventing OOM)
Kumar Gala wrote:
> I'm working on an embedded PPC setup with 64M of memory and no swap.
> I'm trying to figure out how best to tune the VM for an OOM situation
> I'm running into.
>
> I'm running a 2.6.16.35 kernel and have a bittorrent app that appears
> to be initializing a large file for it to download into. What I see
> before running the app:
>
> /bigfoot/usb_disk # cat /proc/meminfo
> MemTotal: 62520 kB
> MemFree: 49192 kB
> Buffers: 8240 kB
> Cached: 740 kB
> SwapCached: 0 kB
> Active: 8196 kB
> Inactive: 1236 kB
> HighTotal: 0 kB
> HighFree: 0 kB
> LowTotal: 62520 kB
> LowFree: 49192 kB
> SwapTotal: 0 kB
> SwapFree: 0 kB
> Dirty: 0 kB
> Writeback: 0 kB
> Mapped: 916 kB
> Slab: 2224 kB
> CommitLimit: 31260 kB
> Committed_AS: 1704 kB
> PageTables: 88 kB
> VmallocTotal: 933872 kB
> VmallocUsed: 9416 kB
> VmallocChunk: 923628 kB
>
> after the OOM:
>
> /bigfoot/usb_disk # cat /proc/meminfo
> MemTotal: 62520 kB
> MemFree: 1608 kB
> Buffers: 8212 kB
> Cached: 42780 kB
> SwapCached: 0 kB
> Active: 6228 kB
> Inactive: 45176 kB
> HighTotal: 0 kB
> HighFree: 0 kB
> LowTotal: 62520 kB
> LowFree: 1608 kB
> SwapTotal: 0 kB
> SwapFree: 0 kB
> Dirty: 35208 kB
> Writeback: 5616 kB
> Mapped: 892 kB
> Slab: 7788 kB
> CommitLimit: 31260 kB
> Committed_AS: 1704 kB
> PageTables: 88 kB
> VmallocTotal: 933872 kB
> VmallocUsed: 9416 kB
> VmallocChunk: 923628 kB
>
> Which makes me think that we aren't writing back fast enough. If I
> mount the drive "sync" the issue clearly goes away.
>
> It appears from an strace we are doing ftruncate64(5, 178257920) when
> we OOM.
>
> Any ideas on VM parameters to tweak so we throttle this from occurring?

You don't give us the actual OOM message. In newer kernels, there has been
quite a bit of work done to improve the OOM situation -- search changelogs
in mm/oom_kill.c mm/vmscan.c mm/page_alloc.c.

--
SUSE Labs, Novell Inc.
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