linux-kernel - Re: [PATCH v4 4/5] mm/shmem: fix infinite loop when swap in shmem error at swapoff time

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Message-ID: <f1af5390-70f1-a231-cc37-c1fc671729d8@huawei.com>
Date:   Tue, 24 May 2022 18:56:39 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "neilb@...e.de" <neilb@...e.de>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "david@...hat.com" <david@...hat.com>,
        "surenb@...gle.com" <surenb@...gle.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "rcampbell@...dia.com" <rcampbell@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/5] mm/shmem: fix infinite loop when swap in shmem
 error at swapoff time

On 2022/5/24 14:44, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Mon, May 23, 2022 at 07:23:53PM +0800, Miaohe Lin wrote:
> ...
>>>
>>> I reproduced the deadloop issues when swapin error occurs at swapoff time in my linux-next-next-20220520 env,
>>> and I found this patch could solve the issue now with the fix in my another email.
>>>
>>> BTW: When I use dm-dust to inject the swapin IO error, I don't see non-uptodate folio when shmem_swapin_folio
>>> and swapoff succeeds. There might be some issues around that module (so I resort to the another way to inject
>>> the swapin error), but the patch itself works anyway. ;)
>>
>> Sorry, the reason I don't see non-uptodate folio when shmem_swapin_folio is that all the shmem pages are still
>> in the swapcache. They're not read from disk so there is no really IO error. :) When they're indeed freed, the
>> deadloop issue occurs.
>>
>> I am thinking about extending the function of MADV_PAGEOUT to free the swapcache page. The page resides in the
>> swapcache does not save the system memory anyway. And this could help test the swapin behavior. But I'm not
>> sure whether it's needed.
> 
> The extension make MADV_PAGEOUT free swapcaches makes sense to me,
> so I'll support it if the original implementer agrees the change.

I'd like trying to do it when I have time. :) Thanks!

> 
> Thanks,
> Naoya Horiguchi
>