From: Andrew Morton <akpm@linux-foundation.org>
To: Laura Abbott <lauraa@codeaurora.org>
Cc: Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-arm-msm@vger.kernel.org
Subject: Re: [RESEND][PATCH v3] mm: Use aligned zone start for pfn_to_bitidx calculation
Date: Mon, 7 Jan 2013 14:31:28 -0800 [thread overview]
Message-ID: <20130107143128.face9220.akpm@linux-foundation.org> (raw)
In-Reply-To: <1357414111-20736-1-git-send-email-lauraa@codeaurora.org>
On Sat, 5 Jan 2013 11:28:31 -0800
Laura Abbott <lauraa@codeaurora.org> wrote:
> The current calculation in pfn_to_bitidx assumes that
> (pfn - zone->zone_start_pfn) >> pageblock_order will return the
> same bit for all pfn in a pageblock. If zone_start_pfn is not
> aligned to pageblock_nr_pages, this may not always be correct.
>
> Consider the following with pageblock order = 10, zone start 2MB:
>
> pfn | pfn - zone start | (pfn - zone start) >> page block order
> ----------------------------------------------------------------
> 0x26000 | 0x25e00 | 0x97
> 0x26100 | 0x25f00 | 0x97
> 0x26200 | 0x26000 | 0x98
> 0x26300 | 0x26100 | 0x98
>
> This means that calling {get,set}_pageblock_migratetype on a single
> page will not set the migratetype for the full block. Fix this by
> rounding down zone_start_pfn when doing the bitidx calculation.
What are the user-visible effects of this bug?
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WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Laura Abbott <lauraa@codeaurora.org>
Cc: Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-arm-msm@vger.kernel.org
Subject: Re: [RESEND][PATCH v3] mm: Use aligned zone start for pfn_to_bitidx calculation
Date: Mon, 7 Jan 2013 14:31:28 -0800 [thread overview]
Message-ID: <20130107143128.face9220.akpm@linux-foundation.org> (raw)
In-Reply-To: <1357414111-20736-1-git-send-email-lauraa@codeaurora.org>
On Sat, 5 Jan 2013 11:28:31 -0800
Laura Abbott <lauraa@codeaurora.org> wrote:
> The current calculation in pfn_to_bitidx assumes that
> (pfn - zone->zone_start_pfn) >> pageblock_order will return the
> same bit for all pfn in a pageblock. If zone_start_pfn is not
> aligned to pageblock_nr_pages, this may not always be correct.
>
> Consider the following with pageblock order = 10, zone start 2MB:
>
> pfn | pfn - zone start | (pfn - zone start) >> page block order
> ----------------------------------------------------------------
> 0x26000 | 0x25e00 | 0x97
> 0x26100 | 0x25f00 | 0x97
> 0x26200 | 0x26000 | 0x98
> 0x26300 | 0x26100 | 0x98
>
> This means that calling {get,set}_pageblock_migratetype on a single
> page will not set the migratetype for the full block. Fix this by
> rounding down zone_start_pfn when doing the bitidx calculation.
What are the user-visible effects of this bug?
next prev parent reply other threads:[~2013-01-07 22:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-05 19:28 [RESEND][PATCH v3] mm: Use aligned zone start for pfn_to_bitidx calculation Laura Abbott
2013-01-05 19:28 ` Laura Abbott
2013-01-07 22:31 ` Andrew Morton [this message]
2013-01-07 22:31 ` Andrew Morton
2013-01-09 17:48 ` Laura Abbott
2013-01-09 17:48 ` Laura Abbott
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