Messages in this thread | | | Date | Fri, 22 Oct 2010 16:08:10 +0200 | From | Jens Axboe <> | Subject | Re: What am I doing wrong? submit_bio() suddenly stops working... |
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On 2010-10-22 15:04, Peter Zijlstra wrote: > On Thu, 2010-10-21 at 20:07 +0200, Jens Axboe wrote: >> >>>> + do { >>>> + bio = bio_alloc(GFP_NOIO, nvecs); >>>> + nvecs >>= 1; >>>> + } while (bio == NULL); >>> >>> This is surly bad. bio_alloc must be allowed to fail >>> (Specially with GFP_NOIO). You should only loop down to >>> 1 and then prepare to return -ENOMEM from this function >>> and handle it properly in callers. (Or schedule and wait >>> like below) >> >> Since __GFP_WAIT is set, it'll never return NULL. And as long as you >> don't allocate more than 1 before doing you submit_bio(), it should be >> OK in this case. > > __GFP_WAIT can return NULL, on OOM and when the size is over a magic > threshold.
The memory allocator, yes, but a mempool backed allocation with __GFP_WAIT cannot. That's the difference.
> I find it bad form to rely on any allocation not failing.
On that we can agree, but it's not always easily doable. I bet you would not like the block layer tossing IOs if it can't get a bio or request structure :-)
-- Jens Axboe
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