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

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Message-ID: <8c5224ce-ba67-2afc-3864-051b8220a87a@suse.com>
Date:   Fri, 21 Dec 2018 16:06:42 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     Matthew Wilcox <willy@...radead.org>
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 21.12.18 г. 15:24 ч., Matthew Wilcox wrote:
> 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?

I thought about that but didn't know if people will complain that some
times in the future we might need it.

>