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DateThu, 06 Jan 2005 16:44:39 +1100
FromNick Piggin <>
SubjectRe: [PATCH][5/?] count writeback pages in nr_scanned
Nick Piggin wrote:
> Andrea Arcangeli wrote:
> 
>> On Thu, Jan 06, 2005 at 04:19:36PM +1100, Nick Piggin wrote:
>>
>>> This is practically what blk_congestion_wait does when the queue
>>> isn't congested though, isn't it?
>>
>>
>>
>> The fundamental difference that makes it reliable is that:
>>
>> 1) only the I/O we're throttling against will be considered for the
>>    wakeup event, which means only clearing PG_writeback will be
>>    considered eligible for wakeup
>>    Currently _all_ unrelated write I/O was considered eligible
>>    for wakeup events and that could cause spurious oom kills.
> 
> 
> I'm not entirely convinced. In Rik's case it didn't matter, because
> all his writeout was in the same zone that reclaim was happening
> against (ZONE_NORMAL), so in that case, PG_writeback throttling
> will do exactly the same thing as blk_congestion_wait.
> 
> I do like your PG_writeback throttling idea for the other reason
> that it should behave better on NUMA systems with lots of zones
> and lots of disks.
> 

... or Andrew's described fix. I think both would result in pretty
similar behaviour, but Andrew's is probably a bit nicer because it
doesn't require the scanner to have initiated the write.
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