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

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Message-ID: <20240828072901.1017792-1-zhaoyang.huang@unisoc.com>
Date: Wed, 28 Aug 2024 15:29:01 +0800
From: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
To: Trond Myklebust <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>,
        <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Zhaoyang Huang
	<huangzhaoyang@...il.com>, <steve.kang@...soc.com>
Subject: [RFC PATCH 1/1] fs: nfs: replace folio_set_private by folio_attach_private

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