linux-kernel - Re: [PATCH v4] btrfs: Use larger zlib buffer for s390 hardware compression

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Message-ID: <20200109011025.GM3929@suse.cz>
Date:   Thu, 9 Jan 2020 02:10:25 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Zaslonko Mikhail <zaslonko@...ux.ibm.com>
Cc:     Josef Bacik <josef@...icpanda.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Eduard Shishkin <edward6@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] btrfs: Use larger zlib buffer for s390 hardware
 compression

On Wed, Jan 08, 2020 at 07:48:31PM +0100, Zaslonko Mikhail wrote:
> >> +        } else if (workspace->strm.avail_out == 0) {
> >> +            /* get another page for the stream end */
> >> +            kunmap(out_page);
> >> +            if (nr_pages == nr_dest_pages) {
> >> +                out_page = NULL;
> >> +                ret = -E2BIG;
> >> +                goto out;
> >> +            }
> >> +            out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
> >> +            if (out_page == NULL) {
> >> +                ret = -ENOMEM;
> >> +                goto out;
> >> +            }
> > 
> > Do we need zlib_deflateEnd() for the above error cases?  Thanks,
> 
> The original btrfs code did not call zlib_deflateEnd() for -E2BIG and 
> -ENOMEM cases, so I stick to the same logic.
> Unlike userspace zlib where deflateEnd() frees all dynamically allocated 
> memory, in the kernel it doesn't do much apart from setting the return 
> code (since all the memory allocations for kernel zlib are performed in advance).

Agreed, deflateEnd is not necessary in the error cases.