linux-kernel - Re: [PATCH] mm: annotate refault stalls from swap

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Date:   Thu, 10 Oct 2019 15:17:47 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sahkeel Butt <shakeelb@...gle.com>,
        Minchan Kim <minchan@...gle.com>
Subject: Re: [PATCH] mm: annotate refault stalls from swap_readpage

On Thu, Oct 10, 2019 at 08:21:34AM -0700, Minchan Kim wrote:
> From: Minchan Kim <minchan@...gle.com>
> 
> If block device supports rw_page operation, it doesn't submit bio
> so annotation in submit_bio for refault stall doesn't work.
> It happens with zram in android, especially swap read path which
> could consume CPU cycle for decompress. It is also a problem for
> zswap which uses frontswap.
> 
> Annotate swap_readpage() to account the synchronous IO overhead
> to prevent underreport memory pressure.
> 
> Cc: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Minchan Kim <minchan@...gle.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>

Can you please add a comment to the caller? Lifted from submit_bio():

	/*
	 * Count submission time as memory stall. When the device is
	 * congested, or the submitting cgroup IO-throttled,
	 * submission can be a significant part of overall IO time.
	 */