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Date: Fri, 21 Dec 2018 05:24:23 -0800
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm: Define VM_(MAX|MIN)_READAHEAD via sizes.h constants
Message-ID: <20181221132423.GA10600@bombadil.infradead.org>
References: <20181221125314.5177-1-nborisov@suse.com>
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Sender: owner-linux-mm@kvack.org
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To: Nikolay Borisov <nborisov@suse.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org

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?