From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Tue, 9 Nov 2004 18:53:29 -0800
From: Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] kswapd shall not sleep during page shortage
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To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: linux-mm@kvack.org, piggin@cyberone.com.au
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Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> 
> > And in that case, they may be
> > holding locks whcih prevent kswapd from being able to do any work either.
> 
> OK... Just out of curiosity:
> Isnt the "lock contention" at this level (filesystem) a relatively rare situation? 
> 

It should be relatively rare - most of the blocking opportunities on the
writepage path should be avoided by now - we bale out, try another page,
throttle on some I/O completion if it's all not working out.

There are probably filesystem allocation semaphores.  journal_start/stop
acts as a semaphore, as does get_request_wait().

It all depends on whether you're looking for common case or worst case.  In
page reclaim we should tune for the common case, and avoid deadlocking in
the worst case.
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