linux-kernel - Re: [PATCH v2 2/3] block: don't hide inode from block

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Message-ID: <194577df-0402-6e3c-3534-af289b5494e0@gmail.com>
Date:   Wed, 13 Oct 2021 19:44:20 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] block: don't hide inode from block_device users

On 10/13/21 16:25, Christoph Hellwig wrote:
> On Wed, Oct 13, 2021 at 09:57:12AM +0100, Pavel Begunkov wrote:
>> Instead of tricks with struct bdev_inode, just openly place the inode
>> inside struct block_device. First, it allows us to inline I_BDEV, which
>> is simple but non-inline nature of it impacts performance. Also, make it
>> possible to get rid of ->bd_inode pointer and hooping with extra
>> indirection, the amount of which became a noticeable problem for the
>> block layer.
> 
> What fast path outside of bdev.c cares about an inlined I_BDEV?

Mildly hot in io_uring w/o fixed files, but that's not peak perf,
but would also be great to get rid of bdev->bd_inode dereference,
e.g. lots of in fops.c.

Are you going to just hid the dereference in helpers or kill it
with some offseting magic?


> I have dusted off patches to reduce (and hopefully eventually kill)
> accesses to bd_inode outside of bdev.c, so this goes into the wrong
> direction.
> 
> If needed I'd rather figure out a way to fix any smoking gun without
> this change.
> 

-- 
Pavel Begunkov