From: Nick Piggin <npiggin@suse.de>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Nick Piggin <npiggin@suse.de>, Andrew Morton <akpm@osdl.org>,
Linux Memory Management <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [patch 5/6] mm: simplify vmscan vs release refcounting
Date: Thu, 19 Jan 2006 20:53:13 +0100 [thread overview]
Message-ID: <20060119195312.GA13887@wotan.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0601191130590.3240@g5.osdl.org>
On Thu, Jan 19, 2006 at 11:35:29AM -0800, Linus Torvalds wrote:
>
>
> On Thu, 19 Jan 2006, Nick Piggin wrote:
> >
> > The VM has an interesting race where a page refcount can drop to zero, but
> > it is still on the LRU lists for a short time. This was solved by testing
> > a 0->1 refcount transition when picking up pages from the LRU, and dropping
> > the refcount in that case.
>
> Heh. Now you keep the count offset, but you also end up removing all the
> comments about it (still) being -1 for free.
>
> And your changelog talks about "atomic_inc_not_zero()" even though the
> code actually does
>
> atomic_add_unless(&page->_count, 1, -1);
>
> which makes it pretty confusing ;)
>
> I also think it's wrong - you've changed put_page_testzero() to use
> "atomic_dec_and_test()", even though the count is based on -1.
>
> So this patch _only_ works together with the next one, and is invalid in
> many ways on its own. You should re-split the de-skew part correctly..
>
Man I'm really happy one of us is awake. Sorry, I'll resend the last two.
Nick
next prev parent reply other threads:[~2006-01-19 19:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-19 19:22 [patch 0/6] mm: optimisations and page ref simplifications Nick Piggin
2006-01-19 19:22 ` [patch 1/6] mm: never ClearPageLRU released pages Nick Piggin
2006-01-19 19:23 ` [patch 2/6] mm: PageLRU no testset Nick Piggin
2006-01-19 19:23 ` [patch 3/6] mm: PageActive " Nick Piggin
2006-01-19 19:23 ` [patch 4/6] mm: less atomic ops Nick Piggin
2006-01-19 19:23 ` [patch 5/6] mm: simplify vmscan vs release refcounting Nick Piggin
2006-01-19 19:35 ` Linus Torvalds
2006-01-19 19:53 ` Nick Piggin [this message]
2006-01-19 19:23 ` [patch 6/6] mm: de-skew page refcounting Nick Piggin
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