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Date: Tue, 24 Aug 2004 17:41:07 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: "Udo A. Steinberg" <us15@os.inf.tu-dresden.de>
CC: Andrew Morton <akpm@osdl.org>, torvalds@osdl.org,
       linux-kernel@vger.kernel.org
Subject: Re: Possible dcache BUG
References: <Pine.LNX.4.44.0408020911300.10100-100000@franklin.wrl.org>	<20040808113930.24ae0273.akpm@osdl.org>	<200408100012.08945.gene.heskett@verizon.net>	<200408102342.12792.gene.heskett@verizon.net>	<Pine.LNX.4.58.0408102044220.1839@ppc970.osdl.org>	<20040810211849.0d556af4@laptop.delusion.de>	<Pine.LNX.4.58.0408102201510.1839@ppc970.osdl.org>	<Pine.LNX.4.58.0408102213250.1839@ppc970.osdl.org>	<20040812180033.62b389db@laptop.delusion.de>	<Pine.LNX.4.58.0408121813190.1839@ppc970.osdl.org>	<20040820000238.55e22081@laptop.delusion.de>	<20040820001154.0a5cf331.akpm@osdl.org>	<20040820001905.27a9ff8f@laptop.delusion.de>	<4125AD23.4000705@yahoo.com.au> <20040823230824.3c937d88@laptop.delusion.de>
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Udo A. Steinberg wrote:

>On Fri, 20 Aug 2004 17:49:55 +1000 Nick Piggin (NP) wrote:
>
>NP> Can you reproduce the OOM with the following patch please? Then
>NP> send the output.
>
>I reproduced the problem using a slightly different setup to trigger the
>problem faster:  128 MB RAM, 188992 KB swap
>
>Here's the output of the OOM killer with your patch applied:
>
>oom-killer: gfp_mask=0x1d2
>DMA per-cpu:
>cpu 0 hot: low 2, high 6, batch 1
>cpu 0 cold: low 0, high 2, batch 1
>Normal per-cpu:
>cpu 0 hot: low 14, high 42, batch 7
>cpu 0 cold: low 0, high 14, batch 7
>HighMem per-cpu: empty
>
>Free pages:        1316kB (0kB HighMem)
>Active:5281 inactive:23611 dirty:0 writeback:0 unstable:0 free:329 slab:1403 mapped:12232 pagetables:167
>DMA free:712kB min:44kB low:88kB high:132kB active:5076kB inactive:5332kB present:16384kB pages_scanned:10112 all_unreclaimable? yes
>protections[]: 22 178 178
>Normal free:604kB min:312kB low:624kB high:936kB active:16048kB inactive:89112kB present:114688kB pages_scanned:62432 all_unreclaimable? yes
>protections[]: 0 156 156
>HighMem free:0kB min:128kB low:256kB high:384kB active:0kB inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
>protections[]: 0 0 0
>DMA: 0*4kB 3*8kB 13*16kB 1*32kB 1*64kB 1*128kB 1*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 712kB
>Normal: 1*4kB 1*8kB 1*16kB 0*32kB 1*64kB 0*128kB 0*256kB 1*512kB 0*1024kB 0*2048kB 0*4096kB = 604kB
>HighMem: empty
>Swap cache: add 90886, delete 74524, find 4659/4974, race 0+0
>Out of Memory: Killed process 1217 (gphoto2).
>
>

OK, all_unreclaimable caused the scanner to virtually stop. If 
all_unreclaimable
gets set, it throttles the scanning of that zone right back, which in 
turn greatly
lowers the chance that all_unreclaimable will get cleared.

When we get to priority = 0 in try_to_free_pages (ie. close to OOM), it 
might be
worth clearing each zone's all_unreclaimable for this last time 'round 
the loop.