netdev - Re: [PATCH][RFC] network splice receive

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Date:	Fri, 8 Jun 2007 17:19:39 +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 Fri, Jun 08 2007, Evgeniy Polyakov wrote:
> On Fri, Jun 08, 2007 at 04:14:52PM +0200, Jens Axboe (jens.axboe@...cle.com) wrote:
> > Here's a start, for the splice side at least of storing a buf-private
> > entity with the ops.
> 
> :) I tested the same implementation, but I put skb pointer into
> page->private. My approach is not correct, since the same page can hold
> several objects, so if there are several splicers, this will scream.
> I've tested your patch on top of splice-net branch, here is a result:
> 
> [   44.798853] Slab corruption: skbuff_head_cache start=ffff81003b726668, len=192
> [   44.806148] Redzone: 0x9f911029d74e35b/0x9f911029d74e35b.
> [   44.811598] Last user: [<ffffffff803699fd>](kfree_skbmem+0x7a/0x7e)
> [   44.818012] 0b0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6a 6b 6b a5
> [   44.824889] Prev obj: start=ffff81003b726590, len=192
> [   44.829985] Redzone: 0xd84156c5635688c0/0xd84156c5635688c0.
> [   44.835604] Last user: [<ffffffff8036a22c>](__alloc_skb+0x40/0x13f)
> [   44.842010] 000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   44.848896] 010: 20 58 7e 3b 00 81 ff ff 00 00 00 00 00 00 00 00
> [   44.855772] Next obj: start=ffff81003b726740, len=192
> [   44.860868] Redzone: 0x9f911029d74e35b/0x9f911029d74e35b.
> [   44.866314] Last user: [<ffffffff803699fd>](kfree_skbmem+0x7a/0x7e)
> [   44.872721] 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> [   44.879597] 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> 
> 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.

I'm not surprised, it wasn't tested at all - just provides the basic
framework for storing the skb so we can access it on pipe buffer
release.

Lets talk more next week, I'll likely play with this approach on monday.

-- 
Jens Axboe

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