linux-kernel - Re: [PATCH v3] fs/aio: Replace kmap{,_atomic}() with kmap_local

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Date:   Wed, 07 Jun 2023 16:59:13 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Benjamin LaHaise <bcrl@...ck.org>,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        linux-kernel@...r.kernel.org,
        "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jeff Moyer <jmoyer@...hat.com>,
        Kent Overstreet <kent.overstreet@...ux.dev>
Subject: Re: [PATCH v3] fs/aio: Replace kmap{,_atomic}() with kmap_local_page()

On lunedì 27 marzo 2023 15:22:46 CEST Matthew Wilcox wrote:
> On Mon, Mar 27, 2023 at 12:08:20PM +0200, Fabio M. De Francesco wrote:
> > On giovedì 19 gennaio 2023 17:20:55 CEST Fabio M. De Francesco wrote:
> > > The use of kmap() and kmap_atomic() are being deprecated in favor of
> > > kmap_local_page().
> > >
> > > [...]
> > >
> > > Therefore, replace kmap() and kmap_atomic() with kmap_local_page() in
> > > fs/aio.c.
>
> Or should we just stop allocating aio rings from HIGHMEM and remove
> the calls to kmap()?  How much memory are we talking about here?

Matthew,

Well, I'll do as you suggested. Actually, I should have made this change when 
you suggested it but... well, I think you can easily guess why I did not.

Here it seems that a call of find_or_create_pages() with the GFP_USER flag
instead of GFP_HIGHUSER is all that is required. And then I'll get rid of the
mappings in favor of some straight page_address().

I just gave a look after months, so I could very well have missed something 
else. If what I just saw it's all that must be changed, I'll send the new 
patch by tomorrow.

Thanks,

Fabio

P.S.: I had sent other patches that must also be changed according to a 
similar comment you made. Obviously, I'll work also on them (no matter if you 
can't probably recall the short series to fs/ufs I'm referring to).