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Date: Thu, 14 Jul 2022 08:25:20 +0800
From: Wang Yugui <wangyugui@...-tech.com>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
David Sterba <dsterba@...e.com>,
Nick Terrell <terrelln@...com>, linux-btrfs@...r.kernel.org,
linux-kernel@...r.kernel.org, Filipe Manana <fdmanana@...nel.org>,
Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c
Hi,
Compiler warning:
fs/btrfs/zstd.c:478:55: warning: passing argument 1 of ‘__kunmap_local’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
478 | kunmap_local(workspace->in_buf.src);
./include/linux/highmem-internal.h:284:24: note: in definition of macro ‘kunmap_local’
284 | __kunmap_local(__addr); \
| ^~~~~~
./include/linux/highmem-internal.h:200:41: note: expected ‘void *’ but argument is of type ‘const void *’
200 | static inline void __kunmap_local(void *addr)
| ~~~~~~^~~~
Best Regards
Wang Yugui (wangyugui@...-tech.com)
2022/07/14
> 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@...nel.org>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.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(¶ms, 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
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