linux-ext4 - Re: [PATCH] ext4/xfs: add page refcount helper

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Message-ID: <f8aff11f-3913-a0ac-b8cd-5380738a8e3c@nvidia.com>
Date:   Wed, 7 Oct 2020 11:12:40 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-mm@...ck.org>, <linux-xfs@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-nvdimm@...ts.01.org>,
        <linux-kernel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Alexander Viro" <viro@...iv.linux.org.uk>,
        Theodore Ts'o <tytso@....edu>,
        "Christoph Hellwig" <hch@....de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ext4/xfs: add page refcount helper


On 10/7/20 1:25 AM, Jan Kara wrote:
> On Tue 06-10-20 16:09:30, Ralph Campbell wrote:
>> There are several places where ZONE_DEVICE struct pages assume a reference
>> count == 1 means the page is idle and free. Instead of open coding this,
>> add a helper function to hide this detail.
>>
>> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
>> Reviewed-by: Christoph Hellwig <hch@....de>
> 
> Looks as sane direction but if we are going to abstract checks when
> ZONE_DEVICE page is idle, we should also update e.g.
> mm/swap.c:put_devmap_managed_page() or
> mm/gup.c:__unpin_devmap_managed_user_page() (there may be more places like
> this but I found at least these two...). Maybe Dan has more thoughts about
> this.
> 
> 								Honza

I think this is a good point but I would like to make that a follow on
patch rather than add to this one.