linux-kernel - Re: [PATCH] fs/aio: Stop allocating aio rings from HIGHMEM

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Message-ID: <6488cd9030687_1ad89929456@iweiny-mobl.notmuch>
Date:   Tue, 13 Jun 2023 13:12:00 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, <linux-aio@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] fs/aio: Stop allocating aio rings from HIGHMEM

Fabio M. De Francesco wrote:
> There is no need to allocate aio rings from HIGHMEM because of very
> little memory needed here.
> 
> Therefore, use GFP_USER flag in find_or_create_page() and get rid of
> kmap*() mappings.
> 
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Suggested-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  fs/aio.c | 26 +++++++++-----------------
>  1 file changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index b0b17bd098bb..77e33619de40 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c

[snip]

> @@ -1250,10 +1244,9 @@ static long aio_read_events_ring(struct kioctx *ctx,
>  		avail = min(avail, nr - ret);
>  		avail = min_t(long, avail, AIO_EVENTS_PER_PAGE - pos);
>  
> -		ev = kmap(page);
> +		ev = page_address(page);

NIT: This might be cleaner to remove the temp variable;

		ev = page_address(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE];

But generally LGTM.

Reviewed-by: Ira Weiny <ira.weiny@...el.com>