netdev - Re: [PATCH] net: use non-compound pages in frag allocator

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Message-ID: <1470318647.13693.28.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Thu, 04 Aug 2016 15:50:47 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ilya Lesokhin <ilyal@...lanox.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"edumazet@...gle.com" <edumazet@...gle.com>
Subject: Re: [PATCH] net: use non-compound pages in frag allocator

On Thu, 2016-08-04 at 13:38 +0000, Ilya Lesokhin wrote:
> You are right I just realized that this patch causes a memory leak, so sorry for the spam.
> 
> I just had problem understanding when compound pages are needed and when It is enough to use an high order pages.
> I thought that that high order pages are enough for this use case, tested it and saw no problems.
> 
> Unfortunately it seems you must use compound pages to keep track of  the page order.
> put_page assumes that the order of a non-compound page is always 0. 
> It would be nice to document it somewhere but I'm not sure where.

Please do not top-post on netdev mailing list.

( Documentation/development-process/2.Process : line 422 )

AFAIK, only when we can call free_pages(p, order) and provide @order, we
can avoid using __GFP_COMP at alloc time.

But if some path has to use put_page(), then we are forced to use
__GFP_COMP for high order pages.

Thanks.