linux-kernel - Re: [RFC PATCH v2 1/3] btrfs: Convert zlib_decompress_bio() to use kmap_local

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Date:   Fri, 17 Jun 2022 20:51:03 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Nick Terrell <terrelln@...com>,
        Chris Down <chris@...isdown.name>,
        Filipe Manana <fdmanana@...e.com>, Qu Wenruo <wqu@...e.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Gabriel Niebler <gniebler@...e.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/3] btrfs: Convert zlib_decompress_bio() to use
 kmap_local_page()



On 2022/6/17 20:05, Fabio M. De Francesco wrote:
> 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 zlib_decompress_bio()
> because in this function the mappings are per thread and are not visible
> in other contexts.
>
> Tested with xfstests on QEMU + KVM 32 bits VM with 4GB of RAM and
> HIGHMEM64G enabled. This patch passes 26/26 tests of group "compress".
>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>

Reviewed-by: Qu Wenruo <wqu@...e.com>

Thanks,
Qu
> ---
>   fs/btrfs/zlib.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
> index 767a0c6c9694..770c4c6bbaef 100644
> --- a/fs/btrfs/zlib.c
> +++ b/fs/btrfs/zlib.c
> @@ -287,7 +287,7 @@ int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
>   	unsigned long buf_start;
>   	struct page **pages_in = cb->compressed_pages;
>
> -	data_in = kmap(pages_in[page_in_index]);
> +	data_in = kmap_local_page(pages_in[page_in_index]);
>   	workspace->strm.next_in = data_in;
>   	workspace->strm.avail_in = min_t(size_t, srclen, PAGE_SIZE);
>   	workspace->strm.total_in = 0;
> @@ -309,7 +309,7 @@ int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
>
>   	if (Z_OK != zlib_inflateInit2(&workspace->strm, wbits)) {
>   		pr_warn("BTRFS: inflateInit failed\n");
> -		kunmap(pages_in[page_in_index]);
> +		kunmap_local(data_in);
>   		return -EIO;
>   	}
>   	while (workspace->strm.total_in < srclen) {
> @@ -336,13 +336,13 @@ int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
>
>   		if (workspace->strm.avail_in == 0) {
>   			unsigned long tmp;
> -			kunmap(pages_in[page_in_index]);
> +			kunmap_local(data_in);
>   			page_in_index++;
>   			if (page_in_index >= total_pages_in) {
>   				data_in = NULL;
>   				break;
>   			}
> -			data_in = kmap(pages_in[page_in_index]);
> +			data_in = kmap_local_page(pages_in[page_in_index]);
>   			workspace->strm.next_in = data_in;
>   			tmp = srclen - workspace->strm.total_in;
>   			workspace->strm.avail_in = min(tmp, PAGE_SIZE);
> @@ -355,7 +355,7 @@ int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
>   done:
>   	zlib_inflateEnd(&workspace->strm);
>   	if (data_in)
> -		kunmap(pages_in[page_in_index]);
> +		kunmap_local(data_in);
>   	if (!ret)
>   		zero_fill_bio(cb->orig_bio);
>   	return ret;