From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed, 10 Nov 2004 16:14:50 -0200
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Subject: Re: [PATCH] kswapd shall not sleep during page shortage
Message-ID: <20041110181450.GB12867@logos.cnet>
References: <20041109164642.GE7632@logos.cnet> <20041109121945.7f35d104.akpm@osdl.org> <20041109174125.GF7632@logos.cnet> <20041109133343.0b34896d.akpm@osdl.org> <20041109182622.GA8300@logos.cnet> <20041109142257.1d1411e1.akpm@osdl.org> <20041109203143.GC8414@logos.cnet> <20041109162801.7f7ca242.akpm@osdl.org>
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To: Andrew Morton <akpm@osdl.org>
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On Tue, Nov 09, 2004 at 04:28:01PM -0800, Andrew Morton wrote:
> Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
> >
> > Back to arguing in favour of my patch - it seemed to me that kswapd could 
> >  go to sleep leaving allocators which can't reclaim pages themselves in a 
> >  bad situation. 
> 
> Yes, but those processes would be sleeping in blk_congestion_wait() during,
> say, a GFP_NOIO/GFP_NOFS allocation attempt.  And in that case, they may be
> holding locks whcih prevent kswapd from being able to do any work either.
> 
> >  It would have to be waken up by another instance of alloc_pages to then 
> >  execute and start doing its job, while if it was executing already (madly 
> >  scanning as you say), the chance it would find freeable pages quite
> >  earlier.
> > 
> >  Note that not only disk IO can cause pages to become freeable. A user
> >  can give up its reference on pagecache page for example (leaving
> >  the page on LRU to be found and freed by kswapd).
> 
> yup.  Or munlock(), or direct-io completion.

Andrew,

Shouldnt the kernel ideally clear zone->all_unreclaimable in those 
situations? (munlock, direct-io completion, last reference on pagecache
page, etc).
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