linux-kernel - Re: [PATCH] fdtable: Avoid triggering OOMs from alloc

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Message-ID: <878utqlnf4.fsf@xmission.com>
Date:	Tue, 04 Feb 2014 10:53:35 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Cong Wang <cwang@...pensource.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH] fdtable: Avoid triggering OOMs from alloc_fdmem

Cong Wang <cwang@...pensource.com> writes:

> On Mon, Feb 3, 2014 at 9:26 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>> diff --git a/fs/file.c b/fs/file.c
>> index 771578b33fb6..db25c2bdfe46 100644
>> --- a/fs/file.c
>> +++ b/fs/file.c
>> @@ -34,7 +34,7 @@ static void *alloc_fdmem(size_t size)
>>          * vmalloc() if the allocation size will be considered "large" by the VM.
>>          */
>>         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
>> -               void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
>> +               void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY);
>>                 if (data != NULL)
>>                         return data;
>>         }
>
> Or try again without __GFP_NORETRY like we do in nelink mmap?

I think I would much rather keep the current semantics of return -ENOMEM
and keep the problem localized then trigger a box wide OOM thank you
very much.


Retrying the kmalloc without __GFP_NORETRY is pointless.  If you are in
the unlikely 0.01% of the time when the kmalloc fails it is almost
certainly going to fail again.  Writing out_of_memory() as kmalloc()
is pointless and very confusing.

The vmalloc won't fail unless you are on a 32bit box.  So it isn't a
case that anyone has to deal with in practice.

Eric
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