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: <20220524064416.GB774480@hori.linux.bs1.fc.nec.co.jp>
Date:   Tue, 24 May 2022 06:44:16 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.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 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.

Thanks,
Naoya Horiguchi