linux-kernel - Re: [PATCH 1/1] block: Set same_page to false in __bio_try_merge

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Date:   Thu, 27 Aug 2020 11:44:06 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, axboe@...nel.dk,
        Christoph Hellwig <hch@...radead.org>,
        Shivaprasad G Bhat <sbhat@...ux.ibm.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/1] block: Set same_page to false in __bio_try_merge_page
 if ret is false

Hello Jens,

On 8/21/20 11:41 PM, Ritesh Harjani wrote:
> If we hit the UINT_MAX limit of bio->bi_iter.bi_size and so we are anyway
> not merging this page in this bio, then it make sense to make same_page
> also as false before returning.
> 
> Without this patch, we hit below WARNING in iomap.
> This mostly happens with very large memory system and / or after tweaking
> vm dirty threshold params to delay writeback of dirty data.
> 
> WARNING: CPU: 18 PID: 5130 at fs/iomap/buffered-io.c:74 iomap_page_release+0x120/0x150
>   CPU: 18 PID: 5130 Comm: fio Kdump: loaded Tainted: G        W         5.8.0-rc3 #6
>   Call Trace:
>    __remove_mapping+0x154/0x320 (unreliable)
>    iomap_releasepage+0x80/0x180
>    try_to_release_page+0x94/0xe0
>    invalidate_inode_page+0xc8/0x110
>    invalidate_mapping_pages+0x1dc/0x540
>    generic_fadvise+0x3c8/0x450
>    xfs_file_fadvise+0x2c/0xe0 [xfs]
>    vfs_fadvise+0x3c/0x60
>    ksys_fadvise64_64+0x68/0xe0
>    sys_fadvise64+0x28/0x40
>    system_call_exception+0xf8/0x1c0
>    system_call_common+0xf0/0x278
> 
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Reported-by: Shivaprasad G Bhat <sbhat@...ux.ibm.com>
> Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>

Sorry, I forgot to add the fixes tag. I think below commit
have introduced this. Let me know if you want me to
re-send this patch with below fixes tag.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cc90bc68422318eb8e75b15cd74bc8d538a7df29


-ritesh