linux-kernel - Re: [patch 3/3 -mmotm] oom: invoke oom killer for __GFP

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Message-ID: <4A26FF42.1020104@chelsio.com>
Date:	Wed, 03 Jun 2009 15:54:58 -0700
From:	Divy Le Ray <divy@...lsio.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Rientjes <rientjes@...gle.com>, npiggin@...e.de,
	a.p.zijlstra@...llo.nl, riel@...hat.com, mel@....ul.ie,
	cl@...ux-foundation.org, dave@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [patch 3/3 -mmotm] oom: invoke oom killer for __GFP_NOFAIL

Andrew Morton wrote:
> On Wed, 3 Jun 2009 15:10:38 -0700 (PDT)
> David Rientjes <rientjes@...gle.com> wrote:
>
>   
>> On Tue, 2 Jun 2009, David Rientjes wrote:
>>
>>     
>>> With my patch, we kill a memory hogging task that will free some memory so 
>>> the allocation will succeed (or multiple tasks if insufficient contiguous 
>>> memory is available).  Kernel allocations use __GFP_NOFAIL, so the fault 
>>> of this memory freeing is entirely on the caller, not the page allocator.
>>>
>>> My preference for handling this is to merge my patch (obviously :), and 
>>> then hopefully deprecate __GFP_NOFAIL as much as possible although I don't 
>>> suspect it could be eradicated forever.
>>>
>>>       
>> I really hope this patch isn't getting dropped because it fixes the 
>> possibility that a __GFP_NOFAIL allocation will fail when its definition 
>> is to the contrary.  Depending on the size of the allocation, that can 
>> cause a panic in at least the reiserfs, ntfs, cxgb3, and gfs2 cases.
>>
>> As I mentioned before, it's a noble goal to deprecate __GFP_NOFAIL as much 
>> as possible and (at the least) prevent it from trying high-order 
>> allocation attempts.  The current implementation of the flag is 
>> problematic, however, and this patch addresses it by attempting to free 
>> some memory when direct reclaim fails.
>>
>>     
>
> Sigh, all right, but we suck.
>
> Divy, could we please at least remove __GFP_NOFAIL from
> drivers/net/cxgb?  It's really quite inappropriate for a driver to
> assume that core VM can do magic.  Drivers should test the return value
> and handle the -ENOMEM in the old-fashioned way, please.
>   

We started working on it, and got to eliminate them out of 
cxgb3_main.c::init_tp_parity().
We're still looking at eliminating its use in 
cxgb3_offload.c::t3_process_tid_release_list().
I'll post the patches as soon as they are ready.

cheers,
Divy

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