linux-ext4 - Re: [PATCH] ext4: unlock unused_pages timely when doing writeback

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Message-ID: <20190211045429.GI23000@mit.edu>
Date:   Sun, 10 Feb 2019 23:54:29 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>
CC:     <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: unlock unused_pages timely when doing writeback

On Tue, Jan 29, 2019 at 10:05:31AM +0800, Xiaoguang Wang wrote:
> In mpage_add_bh_to_extent(), when accumulated extents length is greater
> than MAX_WRITEPAGES_EXTENT_LEN or buffer head's b_stat is not equal, we
> will not continue to search unmapped area for this page, but note this
> page is locked, and will only be unlocked in mpage_release_unused_pages()
> after ext4_io_submit, if io also is throttled by blk-throttle or similar
> io qos, we will hold this page locked for a while, it's unnecessary.
> 
> I think the best fix is to refactor mpage_add_bh_to_extent() to let it
> return some hints whether to unlock this page, but given that we will
> improve dioread_nolock later, we can let it done later, so currently
> the simple fix would just call mpage_release_unused_pages() before
> ext4_io_submit().
> 
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>

Thanks, applied.

					- Ted