From: Nikita Danilov <nikita@clusterfs.com>
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Date: Sat, 6 Nov 2004 19:54:12 +0300
To: Andrea Arcangeli <andrea@novell.com>
Cc: Nick Piggin <piggin@cyberone.com.au>, Jesse Barnes <jbarnes@sgi.com>,
       Marcelo Tosatti <marcelo.tosatti@cyclades.com>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
Subject: Re: [PATCH] Remove OOM killer from try_to_free_pages / all_unreclaimable braindamage
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Andrea Arcangeli writes:
 > On Sat, Nov 06, 2004 at 02:37:05PM +0300, Nikita Danilov wrote:
 > > We need page-reservation API of some sort. There were several attempts
 > > to introduce this, but none get into mainline.
 > 
 > they're already in under the name of mempools

I am talking about slightly different thing. Think of some operation
that calls find_or_create_page(). find_or_create_page() doesn't know
about memory reserved in mempools, it uses alloc_page() directly. If one
wants to guarantee that compound operation has enough memory to
complete, memory should be reserved at the lowest level---in the page
allocator.

 > 
 > I'm perfectly aware the fs tends to be the less correct places in terms
 > of allocations, and luckily it's not an heavy memory user, so I still

Either you are kidding, or we are facing very different workloads. In
the world of file-system development, file-system is (not surprisingly)
single largest memory consumer.

 > have to see a deadlock in getblk or create_buffers or similar. It's
 > mostly a correctness issue (math proof it can't deadlock, right now it
 > can if more tasks all get stuck in getblk at the same time during a hard
 > oom condition etc..).

Add here mmap that can dirty all physical memory behind your back, and
delayed disk block allocation that forces ->writepage() to allocate
potentially huge extent when memory is already tight and hope of having
a proof becomes quite remote.

Nikita.
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