linux-kernel - Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86

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Date:   Wed, 29 Mar 2017 02:30:56 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Shaohua Li <shli@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP
 size on x86_64

On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> In this patch, the size of the swap cluster is changed to that of the
> THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
> the THP swap support on x86_64.  Where one swap cluster will be used to
> hold the contents of each THP swapped out.  And some information of the
> swapped out THP (such as compound map count) will be recorded in the
> swap_cluster_info data structure.
> 
> For other architectures which want THP swap support,
> ARCH_USES_THP_SWAP_CLUSTER need to be selected in the Kconfig file for
> the architecture.

Intreseting case could be architecture with HPAGE_PMD_NR < 256.
Can current code pack more than one THP per claster.

If not we need to have BUILG_BUG_ON() to catch attempt of such enabling.

-- 
 Kirill A. Shutemov