linux-kernel - [PATCH 1/3] btrfs: Replace kmap() with kmap_local

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Message-Id: <20220531145335.13954-2-fmdefrancesco@gmail.com>
Date:   Tue, 31 May 2022 16:53:33 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Subject: [PATCH 1/3] btrfs: Replace kmap() with kmap_local_page() in inode.c

The use of kmap() is being deprecated in favor of kmap_local_page() where
it is feasible. With kmap_local_page(), the mapping is per thread, CPU
local and not globally visible.

Therefore, use kmap_local_page() / kunmap_local() in inode.c wherever the
mappings are per thread and not globally visible.

Tested on QEMU + KVM 32 bits VM with 4GB of RAM and HIGHMEM64G enabled.

Suggested-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 fs/btrfs/inode.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 81737eff92f3..7d84d57a0653 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -10779,15 +10779,15 @@ ssize_t btrfs_do_encoded_write(struct kiocb *iocb, struct iov_iter *from,
 			ret = -ENOMEM;
 			goto out_pages;
 		}
-		kaddr = kmap(pages[i]);
+		kaddr = kmap_local_page(pages[i]);
 		if (copy_from_iter(kaddr, bytes, from) != bytes) {
-			kunmap(pages[i]);
+			kunmap_local(kaddr);
 			ret = -EFAULT;
 			goto out_pages;
 		}
 		if (bytes < PAGE_SIZE)
 			memset(kaddr + bytes, 0, PAGE_SIZE - bytes);
-		kunmap(pages[i]);
+		kunmap_local(kaddr);
 	}
 
 	for (;;) {
-- 
2.36.1