linux-kernel - Re: [PATCH -mm] mm, swap: Fix false error message in __swp

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Date:   Wed, 25 Oct 2017 05:17:08 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>, stable@...r.kernel.org,
        Christian Kujau <lists@...dbynature.de>
Subject: Re: [PATCH -mm] mm, swap: Fix false error message in
 __swp_swapcount()

On Tue, Oct 24, 2017 at 10:47:00AM +0800, Huang, Ying wrote:
> From: Ying Huang <ying.huang@...el.com>
> 
> __swp_swapcount() is used in __read_swap_cache_async().  Where the
> invalid swap entry (offset > max) may be supplied during swap
> readahead.  But __swp_swapcount() will print error message for these
> expected invalid swap entry as below, which will make the users
> confusing.
> 
>   swap_info_get: Bad swap offset entry 0200f8a7
> 
> So the swap entry checking code in __swp_swapcount() is changed to
> avoid printing error message for it.  To avoid to duplicate code with
> __swap_duplicate(), a new helper function named
> __swap_info_get_silence() is added and invoked in both places.

It's the problem caused by readahead, not __swap_info_get which is low-end
primitive function. Instead, please fix high-end swapin_readahead to limit
to last valid block as handling to avoid swap header which is special case,
too.