linux-kernel - Re: [PATCH 01/10] zsmalloc: fix init

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Date:	Mon, 15 Sep 2014 08:24:27 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Nitin Gupta <ngupta@...are.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 01/10] zsmalloc: fix init_zspage free obj linking

On Fri, Sep 12, 2014 at 12:43:22PM -0400, Dan Streetman wrote:
> On Fri, Sep 12, 2014 at 12:59 AM, Minchan Kim <minchan@...nel.org> wrote:
> > On Thu, Sep 11, 2014 at 04:53:52PM -0400, Dan Streetman wrote:
> >> When zsmalloc creates a new zspage, it initializes each object it contains
> >> with a link to the next object, so that the zspage has a singly-linked list
> >> of its free objects.  However, the logic that sets up the links is wrong,
> >> and in the case of objects that are precisely aligned with the page boundries
> >> (e.g. a zspage with objects that are 1/2 PAGE_SIZE) the first object on the
> >> next page is skipped, due to incrementing the offset twice.  The logic can be
> >> simplified, as it doesn't need to calculate how many objects can fit on the
> >> current page; simply checking the offset for each object is enough.
> >
> > If objects are precisely aligned with the page boundary, pages_per_zspage
> > should be 1 so there is no next page.
> 
> ah, ok.  I wonder if it should be changed anyway so it doesn't rely on
> that detail, in case that's ever changed in the future.  It's not
> obvious the existing logic relies on that for correct operation.  And
> this simplifies the logic too.

Correct description and resend if you want.

-- 
Kind regards,
Minchan Kim
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