linux-ext4 - Re: [RFC 0/5] Ext4: Add support for blocksize < pagesize for dioread

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Message-ID: <20191106172302.GE12685@quack2.suse.cz>
Date:   Wed, 6 Nov 2019 18:23:02 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     tytso@....edu, jack@...e.cz, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, mbobrowski@...browski.org
Subject: Re: [RFC 0/5] Ext4: Add support for blocksize < pagesize for
 dioread_nolock

On Wed 16-10-19 13:07:06, Ritesh Harjani wrote:
> This patch series adds the support for blocksize < pagesize for
> dioread_nolock feature.
> 
> Since in case of blocksize < pagesize, we can have multiple
> small buffers of page as unwritten extents, we need to
> maintain a vector of these unwritten extents which needs
> the conversion after the IO is complete. Thus, we maintain
> a list of tuple <offset, size> pair (io_end_vec) for this &
> traverse this list to do the unwritten to written conversion.
> 
> Appreciate any reviews/comments on this patches.

I know Ted has merged the patches already so this is just informational but
I've read the patches and they look fine to me. Thanks for the work! I was
just thinking that we could actually make the vector tracking more
efficient because the io_end always looks like:

one-big-extent-to-fully-write + whatever it takes to fully write out the
last page

So your vectors could be also expressed as "extent to write" + bitmap of
blocks written in the last page. And 64-bits are enough for the bitmap for
anything ext4 supports so we could easily save allocation of ioend_vec etc.
Just a suggestion.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR