linux-kernel - Re: [PATCH] mm: Define VM_(MAX|MIN)

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Date:   Fri, 21 Dec 2018 05:24:23 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] mm: Define VM_(MAX|MIN)_READAHEAD via sizes.h constants

On Fri, Dec 21, 2018 at 02:53:14PM +0200, Nikolay Borisov wrote:
> All users of the aformentioned macros convert them to kbytes by
> multplying. Instead, directly define the macros via the aptly named
> SZ_16K/SZ_128K ones. Also remove the now redundant comments explaining
> that VM_* are defined in kbytes it's obvious. No functional changes.

Actually, all users of these constants convert them to pages!

> +	q->backing_dev_info->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
> +		sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
> +	sb->s_bdi->ra_pages	= VM_MAX_READAHEAD / PAGE_SIZE;
> +	sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
> +	sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;

> -#define VM_MAX_READAHEAD	128	/* kbytes */
> -#define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
> +#define VM_MAX_READAHEAD	SZ_128K
> +#define VM_MIN_READAHEAD	SZ_16K	/* includes current page */

So perhaps:

#define VM_MAX_READAHEAD	(SZ_128K / PAGE_SIZE)

VM_MIN_READAHEAD isn't used, so just delete it?