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Date:   Wed, 10 Aug 2022 16:14:48 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Jiri Slaby <jslaby@suse.cz>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        jack@suse.com, adilger.kernel@dilger.ca, tytso@mit.edu,
        stable@vger.kernel.org, Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Alexey Romanov <avromanov@sberdevices.ru>,
        Dmitry Rokosov <ddrokosov@sberdevices.ru>,
        Lukas Czerner <lczerner@redhat.com>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH] Revert "zram: remove double compression logic"
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References: <YvJKwCXewHmuWGdh@google.com>
 <20220810070609.14402-1-jslaby@suse.cz>
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On (22/08/10 09:06), Jiri Slaby wrote:
> This reverts commit e7be8d1dd983156bbdd22c0319b71119a8fbb697 as it
> causes zram failures. It does not revert cleanly, PTR_ERR handling was
> introduced in the meantime. This is handled by appropriate IS_ERR.
> 
> When under memory pressure, zs_malloc() can fail. Before the above
> commit, the allocation was retried with direct reclaim enabled
> (GFP_NOIO). After the commit, it is not -- only __GFP_KSWAPD_RECLAIM is
> tried.
> 
> So when the failure occurs under memory pressure, the overlaying
> filesystem such as ext2 (mounted by ext4 module in this case) can emit
> failures, making the (file)system unusable:
>   EXT4-fs warning (device zram0): ext4_end_bio:343: I/O error 10 writing to inode 16386 starting block 159744)
>   Buffer I/O error on device zram0, logical block 159744
> 
> With direct reclaim, memory is really reclaimed and allocation succeeds,
> eventually. In the worst case, the oom killer is invoked, which is
> proper outcome if user sets up zram too large (in comparison to
> available RAM).
> 
> This very diff doesn't apply to 5.19 (stable) cleanly (see PTR_ERR note
> above). Use revert of e7be8d1dd983 directly.
> 
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1202203
> Fixes: e7be8d1dd983 ("zram: remove double compression logic")
> Cc: stable@vger.kernel.org # 5.19
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
> Cc: Alexey Romanov <avromanov@sberdevices.ru>
> Cc: Dmitry Rokosov <ddrokosov@sberdevices.ru>
> Cc: Lukas Czerner <lczerner@redhat.com>
> Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>