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Date: Tue, 12 Jun 2007 13:33:54 +0200 From: Jens Axboe <jens.axboe@...cle.com> To: Evgeniy Polyakov <johnpol@....mipt.ru> Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH][RFC] network splice receive On Tue, Jun 12 2007, Evgeniy Polyakov wrote: > On Sat, Jun 09, 2007 at 08:36:09AM +0200, Jens Axboe (jens.axboe@...cle.com) wrote: > > On Fri, Jun 08 2007, Evgeniy Polyakov wrote: > > > On Fri, Jun 08, 2007 at 06:57:25PM +0400, Evgeniy Polyakov (johnpol@....mipt.ru) wrote: > > > > I will try some things for the nearest 30-60 minutes, and then will move to > > > > canoe trip until thuesday, so will not be able to work on this idea. > > > > > > Ok, replacing in fs/splice.c every page_cache_release() with > > > static void splice_page_release(struct page *p) > > > { > > > if (!PageSlab(p)) > > > page_cache_release(p); > > > } > > > > Ehm, I don't see why that should be necessary. Except in > > splice_to_pipe(), I have considered that we need to pass in a release > > function if mapping fails at some point. But it's probably best to do > > that in the caller, since they have the knowledge of how to release the > > pages. > > > > The rest of the PageSlab() tests are bogus. > > I had a crashdump, where page was released via splice_to_pipe() indeed, > I did not investigate if it is possible to release provided page in > other places. I think if in future there will other slab usage cases > except networking receiving, that might be useful, but as is it is not > needed. Read the just posted code, it has moved way beyond this :-) > > > and putting cloned skb into private field instead of > > > original on in spd_fill_page() ends up without kernel hung. > > > > Why? Seems pointless to allocate a clone just to hold on to the skb, a > > reference should be equally good. I would not be opposed to doing it > > this way, I just don't see what a clone buys us as compared to just > > holding that reference to the skb. > > Receiving code does not expect shared skbs - too many fields are changed > with assumptions that it is a private copy. Actually the main problem is that tcp_read_sock() unconditionally frees the skb, so it wouldn't help if we grabbed a reference to it. I've yet to receive an explanation of why it does so, seem awkward and violates the whole principle of reference counted objects. Davem?? So for now, skb_splice_bits() clones the incoming skb to avoid that. I'd hope we can get rid of that by fixing tcp_read_sock(), though. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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