linux-kernel - Re: [patch] mm, thp: fix defrag setting if newline is not used

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Message-Id: <20200116191609.3972fd5301cf364a27381923@linux-foundation.org>
Date:   Thu, 16 Jan 2020 19:16:09 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, thp: fix defrag setting if newline is not used

On Tue, 14 Jan 2020 17:58:36 -0800 (PST) David Rientjes <rientjes@...gle.com> wrote:

> If thp defrag setting "defer" is used and a newline is *not* used when
> writing to the sysfs file, this is interpreted as the "defer+madvise"
> option.
> 
> This is because we do prefix matching and if five characters are written
> without a newline, the current code ends up comparing to the first five
> bytes of the "defer+madvise" option and using that instead.
> 
> Find the length of what the user is writing and use that to guide our
> decision on which string comparison to do.

Gee, why is this code so complicated?  Can't we just do

	if (sysfs_streq(buf, "always")) {
		...
	} else if sysfs_streq(buf, "defer+madvise")) {
		...
	}
	...