linux-kernel - Re: [syzbot] [mm?] BUG: Bad page map (7)

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Date:   Wed, 20 Sep 2023 09:29:18 +0800
From:   Yin Fengwei <fengwei.yin@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Matthew Wilcox <willy@...radead.org>
CC:     syzbot <syzbot+55cc72f8cc3a549119df@...kaller.appspotmail.com>,
        <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] [mm?] BUG: Bad page map (7)



On 9/20/23 00:11, Dave Hansen wrote:
> On 9/18/23 18:11, Yin Fengwei wrote:
>>> I will find a test machine to measure the performance difference of these two
>>> versions by using xfs + will-it-scale. Will keep you guys updated.
>> I'd like to move this bug fixing forward. Based on the test result here:
>> https://lore.kernel.org/linux-mm/124631ab-eb4c-6584-12d4-f3c91e69c873@intel.com/
>> There is very small performance delta between your version and Dave's.
>>
>> What do you think if we propose to merge Dave's version? Or do I need collect
>> more data? Thanks.
> 
> I honestly don't feel that strongly about my version versus Matthew's.
> I like mine, but I'll happily ack either approach.
> 
> The thing I care about the most is getting the bug fixed ... quickly. :)
Same in my side.

Regarding the performance delta is very small, I thought we should follow the
commit message of 6b28baca9b1f0d4a42b865da7a05b1c81424bd5c:
    The invert is done by pte/pmd_modify and pfn/pmd/pud_pte for PROTNONE and
    pte/pmd/pud_pfn undo it.
    
    This assume that no code path touches the PFN part of a PTE directly
    without using these primitives.


Regards
Yin, Fengwei