linux-kernel - Re: [PATCH 1/1] mm/madvise: enhance lazyfreeing with mTHP in madvise

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Message-ID: <3c56d7b8-b76d-4210-b431-ee6431775ba7@intel.com>
Date: Tue, 27 Feb 2024 14:14:42 +0800
From: Yin Fengwei <fengwei.yin@...el.com>
To: Barry Song <21cnbao@...il.com>
CC: Ryan Roberts <ryan.roberts@....com>, Lance Yang <ioworker0@...il.com>,
	David Hildenbrand <david@...hat.com>, <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <mhocko@...e.com>,
	<minchan@...nel.org>, <peterx@...hat.com>, <shy828301@...il.com>,
	<songmuchun@...edance.com>, <wangkefeng.wang@...wei.com>,
	<zokeefe@...gle.com>
Subject: Re: [PATCH 1/1] mm/madvise: enhance lazyfreeing with mTHP in
 madvise_free



On 2/27/24 10:17, Barry Song wrote:
>> Like if we hit folio which is partially mapped to the range, don't split it but
>> just unmap the mapping part from the range. Let page reclaim decide whether
>> split the large folio or not (If it's not mapped to any other range,it will be
>> freed as whole large folio. If part of it still mapped to other range,page reclaim
>> can decide whether to split it or ignore it for current reclaim cycle).
> Yes, we can. but we still have to play the ptes check game to avoid adding
> folios multiple times to reclaim the list.
> 
> I don't see too much difference between splitting in madvise and splitting
> in vmscan.  as our real purpose is avoiding splitting entirely mapped
> large folios. for partial mapped large folios, if we split in madvise, then
> we don't need to play the game of skipping folios while iterating PTEs.
> if we don't split in madvise, we have to make sure the large folio is only
> added in reclaimed list one time by checking if PTEs belong to the
> previous added folio.

If the partial mapped large folio is unmapped from the range, the related PTE
become none. How could the folio be added to reclaimed list multiple times?


Regards
Yin, Fengwei