linux-kernel - Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios

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Message-ID: <c66b2ce5-6f98-46be-bf0d-3172c17fa0f5@intel.com>
Date: Fri, 19 Apr 2024 22:03:20 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: David Hildenbrand <david@...hat.com>, <linux-kernel@...r.kernel.org>
CC: <linux-mm@...ck.org>, <linux-doc@...r.kernel.org>,
	<cgroups@...r.kernel.org>, <linux-sh@...r.kernel.org>,
	<linux-trace-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>, "Matthew Wilcox (Oracle)"
	<willy@...radead.org>, Peter Xu <peterx@...hat.com>, Ryan Roberts
	<ryan.roberts@....com>, Yang Shi <shy828301@...il.com>, Zi Yan
	<ziy@...dia.com>, Jonathan Corbet <corbet@....net>, Hugh Dickins
	<hughd@...gle.com>, Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich Felker
	<dalias@...c.org>, John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Chris Zankel <chris@...kel.net>, Max Filippov <jcmvbkbc@...il.com>, "Muchun
 Song" <muchun.song@...ux.dev>, Miaohe Lin <linmiaohe@...wei.com>, "Naoya
 Horiguchi" <naoya.horiguchi@....com>, Richard Chang <richardycc@...gle.com>
Subject: Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using
 the mapcount of large folios



On 4/10/2024 3:22 AM, David Hildenbrand wrote:
> We can now read the mapcount of large folios very efficiently. Use it to
> improve our handling of partially-mappable folios, falling back
> to making a guess only in case the folio is not "obviously mapped shared".
> 
> We can now better detect partially-mappable folios where the first page is
> not mapped as "mapped shared", reducing "false negatives"; but false
> negatives are still possible.
> 
> While at it, fixup a wrong comment (false positive vs. false negative)
> for KSM folios.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>