linux-kernel - Re: [PATCH -mm -v3 02/12] mm, THP, swap: Support to reclaim swap space for THP swapped out

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Message-ID: <1501004857.26846.19.camel@redhat.com>
Date:   Tue, 25 Jul 2017 13:47:37 -0400
From:   Rik van Riel <riel@...hat.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>,
        Hugh Dickins <hughd@...gle.com>, Shaohua Li <shli@...nel.org>
Subject: Re: [PATCH -mm -v3 02/12] mm, THP, swap: Support to reclaim swap
 space for THP swapped out

On Mon, 2017-07-24 at 13:18 +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> The normal swap slot reclaiming can be done when the swap count
> reaches SWAP_HAS_CACHE.  But for the swap slot which is backing a
> THP,
> all swap slots backing one THP must be reclaimed together, because
> the
> swap slot may be used again when the THP is swapped out again later.
> So the swap slots backing one THP can be reclaimed together when the
> swap count for all swap slots for the THP reached SWAP_HAS_CACHE.  In
> the patch, the functions to check whether the swap count for all swap
> slots backing one THP reached SWAP_HAS_CACHE are implemented and used
> when checking whether a swap slot can be reclaimed.
> 
> To make it easier to determine whether a swap slot is backing a THP,
> a
> new swap cluster flag named CLUSTER_FLAG_HUGE is added to mark a swap
> cluster which is backing a THP (Transparent Huge Page).  Because THP
> swap in as a whole isn't supported now.  After deleting the THP from
> the swap cache (for example, swapping out finished), the
> CLUSTER_FLAG_HUGE flag will be cleared.  So that, the normal pages
> inside THP can be swapped in individually.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Shaohua Li <shli@...nel.org>
> Cc: Rik van Riel <riel@...hat.com>
> 
Acked-by: Rik van Riel <riel@...hat.com>

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