linux-kernel - Re: [RFC PATCH 1/1] fs: nfs: replace folio_set_private by folio_attach

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Message-ID: <CAGWkznEcqq-ZU6AuCZvyscdCpvR47L_9t+Z8Bb=QrxyL4VAaKg@mail.gmail.com>
Date: Thu, 29 Aug 2024 14:18:22 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Christoph Hellwig <hch@...radead.org>
Cc: Trond Myklebust <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, steve.kang@...soc.com
Subject: Re: [RFC PATCH 1/1] fs: nfs: replace folio_set_private by folio_attach_private

loop more

On Wed, Aug 28, 2024 at 3:29 PM zhaoyang.huang
<zhaoyang.huang@...soc.com> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
>
> This patch is inspired by a code review of fs codes which aims at
> folio's extra refcnt that could introduce unwanted behavious when
> judging refcnt, such as[1]. The change relys on the policy as the
> LRU page with private data should take one corresponding refcnt.
>
> [1]
> long mapping_evict_folio(struct address_space *mapping, struct folio *folio)
> {
> ...
> //current code will misjudge here if there is one pte on the folio which
> is be deemed as the one as folio's private
>         if (folio_ref_count(folio) >
>                         folio_nr_pages(folio) + folio_has_private(folio) + 1)
>                 return 0;
>         if (!filemap_release_folio(folio, 0))
>                 return 0;
>
>         return remove_mapping(mapping, folio);
> }
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> ---
>  fs/nfs/write.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index d074d0ceb4f0..80c6ded5f74c 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -772,8 +772,7 @@ static void nfs_inode_add_request(struct nfs_page *req)
>         nfs_lock_request(req);
>         spin_lock(&mapping->i_private_lock);
>         set_bit(PG_MAPPED, &req->wb_flags);
> -       folio_set_private(folio);
> -       folio->private = req;
> +       folio_attach_private(folio, req);
>         spin_unlock(&mapping->i_private_lock);
>         atomic_long_inc(&nfsi->nrequests);
>         /* this a head request for a page group - mark it as having an
> @@ -797,8 +796,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
>
>                 spin_lock(&mapping->i_private_lock);
>                 if (likely(folio)) {
> -                       folio->private = NULL;
> -                       folio_clear_private(folio);
> +                       folio_detach_private(folio);
>                         clear_bit(PG_MAPPED, &req->wb_head->wb_flags);
>                 }
>                 spin_unlock(&mapping->i_private_lock);
> --
> 2.25.1
>