Messages in this thread | | | Subject | Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has BDI_CAP_SYNC capability | From | Jens Axboe <> | Date | Fri, 11 Aug 2017 08:26:59 -0600 |
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On 08/11/2017 04:46 AM, Christoph Hellwig wrote: > On Wed, Aug 09, 2017 at 08:06:24PM -0700, Dan Williams wrote: >> I like it, but do you think we should switch to sbvec[<constant>] to >> preclude pathological cases where nr_pages is large? > > Yes, please. > > Then I'd like to see that the on-stack bio even matters for > mpage_readpage / mpage_writepage. Compared to all the buffer head > overhead the bio allocation should not actually matter in practice.
I'm skeptical for that path, too. I also wonder how far we could go with just doing a per-cpu bio recycling facility, to reduce the cost of having to allocate a bio. The on-stack bio parts are fine for simple use case, where simple means that the patch just special cases the allocation, and doesn't have to change much else.
I had a patch for bio recycling and batched freeing a year or two ago, I'll see if I can find and resurrect it.
-- Jens Axboe
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