linux-kernel - Re: [PATCH 03/33] mm: slub: add knowledge of reserve pages

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Message-Id: <1193835258.27652.199.camel@twins>
Date:	Wed, 31 Oct 2007 13:54:18 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, trond.myklebust@....uio.no
Subject: Re: [PATCH 03/33] mm: slub: add knowledge of reserve pages

On Wed, 2007-10-31 at 22:25 +1100, Nick Piggin wrote:
> On Wednesday 31 October 2007 23:17, Peter Zijlstra wrote:
> > On Wed, 2007-10-31 at 21:46 +1100, Nick Piggin wrote:
> 
> > > And I'd prevent these ones from doing so.
> > >
> > > Without keeping track of "reserve" pages, which doesn't feel
> > > too clean.
> >
> > The problem with that is that once a slab was allocated with the right
> > allocation context, anybody can get objects from these slabs.
> 
> [snip]
> 
> I understand that.
> 
> 
> > So we either reserve a page per object, which for 32 byte objects is a
> > large waste, or we stop anybody who doesn't have the right permissions
> > from obtaining objects. I took the latter approach.
> 
> What I'm saying is that the slab allocator slowpath should always
> just check watermarks against the current task. Instead of this
> ->reserve stuff.

So what you say is to allocate a slab every time we take the slow path,
even when we already have one?

That sounds rather sub-optimal.

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