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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Nick Terrell <terrelln@fb.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Filipe Manana <fdmanana@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>
Subject: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c
Date:   Sat, 11 Jun 2022 15:52:03 +0200
Message-Id: <20220611135203.27992-1-fmdefrancesco@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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

Therefore, use kmap_local_page() / kunmap_local() in zstd.c because in
this file the mappings are per thread and are not visible in other
contexts; meanwhile refactor zstd_compress_pages() to comply with nested
local mapping / unmapping ordering rules.

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

Cc: Filipe Manana <fdmanana@kernel.org>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---

Thanks to Ira Weiny for his invaluable help and persevering support.
Thanks also to Filipe Manana for identifying a fundamental detail I had overlooked:
https://lore.kernel.org/lkml/20220611093411.GA3779054@falcondesktop/ 

tweed32:/usr/lib/xfstests # ./check -g compress
FSTYP         -- btrfs
PLATFORM      -- Linux/i686 tweed32 5.19.0-rc1-vanilla-debug+ #22 SMP PREEMPT_DYNAMIC Sat Jun 11 14:31:39 CEST 2022
MKFS_OPTIONS  -- /dev/loop1
MOUNT_OPTIONS -- /dev/loop1 /mnt/scratch

btrfs/024 1s ...  0s
btrfs/026 3s ...  3s
btrfs/037 1s ...  1s
btrfs/038 1s ...  0s
btrfs/041 0s ...  1s
btrfs/062 34s ...  35s
btrfs/063 18s ...  18s
btrfs/067 33s ...  32s
btrfs/068 10s ...  10s
btrfs/070       [not run] btrfs and this test needs 5 or more disks in SCRATCH_DEV_POOL
btrfs/071       [not run] btrfs and this test needs 5 or more disks in SCRATCH_DEV_POOL
btrfs/072 33s ...  33s
btrfs/073 17s ...  15s
btrfs/074 36s ...  32s
btrfs/076 0s ...  0s
btrfs/103 1s ...  1s
btrfs/106 1s ...  1s
btrfs/109 1s ...  0s
btrfs/113 0s ...  1s
btrfs/138 43s ...  46s
btrfs/149 1s ...  1s
btrfs/183 1s ...  1s
btrfs/205 1s ...  1s
btrfs/234 3s ...  3s
btrfs/246 0s ...  0s
btrfs/251 1s ...  1s
Ran: btrfs/024 btrfs/026 btrfs/037 btrfs/038 btrfs/041 btrfs/062 btrfs/063 btrfs/067 btrfs/068 btrfs/070 btrfs/071 btrfs/072 btrfs/073 btrfs/074 btrfs/076 btrfs/103 btrfs/106 btrfs/109 btrfs/113 btrfs/138 btrfs/149 btrfs/183 btrfs/205 btrfs/234 btrfs/246 btrfs/251
Not run: btrfs/070 btrfs/071
Passed all 26 tests

 fs/btrfs/zstd.c | 42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
index 0fe31a6f6e68..4d50eb3edce5 100644
--- a/fs/btrfs/zstd.c
+++ b/fs/btrfs/zstd.c
@@ -391,6 +391,8 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 	*out_pages = 0;
 	*total_out = 0;
 	*total_in = 0;
+	workspace->in_buf.src = NULL;
+	workspace->out_buf.dst = NULL;
 
 	/* Initialize the stream */
 	stream = zstd_init_cstream(&params, len, workspace->mem,
@@ -403,7 +405,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 
 	/* map in the first page of input data */
 	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
-	workspace->in_buf.src = kmap(in_page);
+	workspace->in_buf.src = kmap_local_page(in_page);
 	workspace->in_buf.pos = 0;
 	workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
 
@@ -415,7 +417,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		goto out;
 	}
 	pages[nr_pages++] = out_page;
-	workspace->out_buf.dst = kmap(out_page);
+	workspace->out_buf.dst = kmap_local_page(out_page);
 	workspace->out_buf.pos = 0;
 	workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
 
@@ -450,9 +452,9 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		if (workspace->out_buf.pos == workspace->out_buf.size) {
 			tot_out += PAGE_SIZE;
 			max_out -= PAGE_SIZE;
-			kunmap(out_page);
+			kunmap_local(workspace->out_buf.dst);
 			if (nr_pages == nr_dest_pages) {
-				out_page = NULL;
+				workspace->out_buf.dst = NULL;
 				ret = -E2BIG;
 				goto out;
 			}
@@ -462,7 +464,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 				goto out;
 			}
 			pages[nr_pages++] = out_page;
-			workspace->out_buf.dst = kmap(out_page);
+			workspace->out_buf.dst = kmap_local_page(out_page);
 			workspace->out_buf.pos = 0;
 			workspace->out_buf.size = min_t(size_t, max_out,
 							PAGE_SIZE);
@@ -477,15 +479,16 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		/* Check if we need more input */
 		if (workspace->in_buf.pos == workspace->in_buf.size) {
 			tot_in += PAGE_SIZE;
-			kunmap(in_page);
+			kunmap_local(workspace->out_buf.dst);
+			kunmap_local((void *)workspace->in_buf.src);
 			put_page(in_page);
-
 			start += PAGE_SIZE;
 			len -= PAGE_SIZE;
 			in_page = find_get_page(mapping, start >> PAGE_SHIFT);
-			workspace->in_buf.src = kmap(in_page);
+			workspace->in_buf.src = kmap_local_page(in_page);
 			workspace->in_buf.pos = 0;
 			workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
+			workspace->out_buf.dst = kmap_local_page(out_page);
 		}
 	}
 	while (1) {
@@ -510,9 +513,9 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 
 		tot_out += PAGE_SIZE;
 		max_out -= PAGE_SIZE;
-		kunmap(out_page);
+		kunmap_local(workspace->out_buf.dst);
 		if (nr_pages == nr_dest_pages) {
-			out_page = NULL;
+			workspace->out_buf.dst = NULL;
 			ret = -E2BIG;
 			goto out;
 		}
@@ -522,7 +525,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 			goto out;
 		}
 		pages[nr_pages++] = out_page;
-		workspace->out_buf.dst = kmap(out_page);
+		workspace->out_buf.dst = kmap_local_page(out_page);
 		workspace->out_buf.pos = 0;
 		workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
 	}
@@ -538,12 +541,12 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 out:
 	*out_pages = nr_pages;
 	/* Cleanup */
-	if (in_page) {
-		kunmap(in_page);
+	if (workspace->out_buf.dst)
+		kunmap_local(workspace->out_buf.dst);
+	if (workspace->in_buf.src) {
+		kunmap_local((void *)workspace->in_buf.src);
 		put_page(in_page);
 	}
-	if (out_page)
-		kunmap(out_page);
 	return ret;
 }
 
@@ -567,7 +570,7 @@ int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 		goto done;
 	}
 
-	workspace->in_buf.src = kmap(pages_in[page_in_index]);
+	workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
 	workspace->in_buf.pos = 0;
 	workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
 
@@ -603,14 +606,15 @@ int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 			break;
 
 		if (workspace->in_buf.pos == workspace->in_buf.size) {
-			kunmap(pages_in[page_in_index++]);
+			kunmap_local((void *)workspace->in_buf.src);
+			page_in_index++;
 			if (page_in_index >= total_pages_in) {
 				workspace->in_buf.src = NULL;
 				ret = -EIO;
 				goto done;
 			}
 			srclen -= PAGE_SIZE;
-			workspace->in_buf.src = kmap(pages_in[page_in_index]);
+			workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
 			workspace->in_buf.pos = 0;
 			workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
 		}
@@ -619,7 +623,7 @@ int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 	zero_fill_bio(cb->orig_bio);
 done:
 	if (workspace->in_buf.src)
-		kunmap(pages_in[page_in_index]);
+		kunmap_local((void *)workspace->in_buf.src);
 	return ret;
 }
 
-- 
2.36.1