linux-kernel - Re: [PATCH v2 5/5] mm/khugepaged: Convert collapse_pte_mapped

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Date:   Thu, 19 Oct 2023 10:17:03 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Vishal Moola <vishal.moola@...il.com>, <linux-mm@...ck.org>
CC:     <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
        <shy828301@...il.com>
Subject: Re: [PATCH v2 5/5] mm/khugepaged: Convert collapse_pte_mapped_thp()
 to use folios



On 2023/10/19 7:01, Vishal Moola wrote:
> On Wed, Oct 18, 2023 at 01:32:13PM -0700, Vishal Moola (Oracle) wrote:
>> This removes 2 calls to compound_head() and helps convert khugepaged to
>> use folios throughout.
>>
>> Previously, if the address passed to collapse_pte_mapped_thp()
>> corresponded to a tail page, the scan would fail immediately. Using
>> filemap_lock_folio() we can get the corresponding folio back and try to
>> operate on the folio instead.
>>
>> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> 
> Hi Andrew, I've attached a fix patch addressing the syzbot issue.
> It can be squashed into this patch, syzbot tested it on v2 already as
> well.

Hi Vishal, only IS_ERR(folio) is enough since filemap_lock_folio won't 
return NULL.