linux-kernel - Re: [PATCH, RFC] block: set noio context in submit_bio_noacct

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Date: Fri, 26 Jan 2024 14:52:24 +0100
From: Christoph Hellwig <hch@....de>
To: Jens Axboe <axboe@...nel.dk>
Cc: Matthew Wilcox <willy@...radead.org>, Christoph Hellwig <hch@....de>,
	linux-block@...r.kernel.org, tj@...nel.org, jiangshanlai@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH, RFC] block: set noio context in
 submit_bio_noacct_nocheck

On Thu, Jan 25, 2024 at 09:13:37AM -0700, Jens Axboe wrote:
> > Nono, you don't understand.  The plan is to remove GFP_NOIO
> > entirely.  Allocations should be done with GFP_KERNEL while under a
> > memalloc_noio_save().
> 
> I do understand, but thanks for the vote of confidence. Place the
> save/restore higher up, most likely actual IO submission isn't going to
> be the only (or even major) allocation potentially needed for the IO.

NOIO is defined as allocations that will not recurse into the I/O stack.
So for anything block based, entering the block layer is literally
the defined boundary where it should be used below.  So no, wrapping
every submit_bio into a context annotation doesn't make much sense.