linux-kernel - Re: [PATCH] btrfs: Convert zlib_decompress_bio() to use kmap_local

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Message-ID: <Yr4hzN+BTeIQ6ruI@iweiny-desk3>
Date:   Thu, 30 Jun 2022 15:21:00 -0700
From:   Ira Weiny <ira.weiny@...el.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>,
        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>,
        <linux-btrfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] btrfs: Convert zlib_decompress_bio() to use
 kmap_local_page()

On Sat, Jun 18, 2022 at 11:19:01AM +0200, 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>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Reviewed-by: Qu Wenruo <wqu@...e.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  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 2cd4f6fb1537..966e17cea981 100644
> --- a/fs/btrfs/zlib.c
> +++ b/fs/btrfs/zlib.c
> @@ -284,7 +284,7 @@ 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;
> @@ -306,7 +306,7 @@ 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) {
> @@ -333,13 +333,13 @@ 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);
> @@ -352,7 +352,7 @@ 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;
> -- 
> 2.36.1
>