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Date:   Thu, 2 Nov 2017 14:50:19 +0900
From:   Minchan Kim <>
To:     "Huang, Ying" <>
Cc:     Andrew Morton <>,,,
        Huang Ying <>,
        Tim Chen <>,
        Michal Hocko <>,,
        Christian Kujau <>
Subject: Re: [PATCH -mm -V3] mm, swap: Fix false error message in

On Thu, Nov 02, 2017 at 01:42:25PM +0800, Huang, Ying wrote:
> From: Huang Ying <>
> When a page fault occurs for a swap entry, the physical swap readahead
> (not the VMA base swap readahead) may readahead several swap entries
> after the fault swap entry.  The readahead algorithm calculates some
> of the swap entries to readahead via increasing the offset of the
> fault swap entry without checking whether they are beyond the end of
> the swap device and it relys on the __swp_swapcount() and
> swapcache_prepare() to check it.  Although __swp_swapcount() checks
> for the swap entry passed in, it will complain with the error message
> as follow for the expected invalid swap entry.  This may make the end
> users confused.
>   swap_info_get: Bad swap offset entry 0200f8a7
> To fix the false error message, the swap entry checking is added in
> swapin_readahead() to avoid to pass the out-of-bound swap entries and
> the swap entry reserved for the swap header to __swp_swapcount() and
> swapcache_prepare().
> Cc: Tim Chen <>
> Cc: Michal Hocko <>
> Cc: <> # 4.11-4.13
> Fixes: e8c26ab60598 ("mm/swap: skip readahead for unreferenced swap slots")
> Reported-by: Christian Kujau <>
> Suggested-by: Minchan Kim <>
> Signed-off-by: "Huang, Ying" <>
Acked-by: Minchan Kim <>

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