linux-kernel - Re: [PATCH v5 1/6] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE

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Message-ID: <20160922053003.GA27958@js1304-P5Q-DELUXE>
Date:   Thu, 22 Sep 2016 14:30:03 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/6] mm/page_alloc: don't reserve ZONE_HIGHMEM for
 ZONE_MOVABLE request

On Fri, Sep 16, 2016 at 08:44:17AM +0530, Aneesh Kumar K.V wrote:
> js1304@...il.com writes:
> 
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that
> > important to reserve. When ZONE_MOVABLE is used, this problem would
> > theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE
> > allocation request which is mainly used for page cache and anon page
> > allocation. So, fix it.
> >
> > And, defining sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES - 1 size
> > makes code complex. For example, if there is highmem system, following
> > reserve ratio is activated for *NORMAL ZONE* which would be easyily
> > misleading people.
> >
> >  #ifdef CONFIG_HIGHMEM
> >  32
> >  #endif
> >
> > This patch also fix this situation by defining sysctl_lowmem_reserve_ratio
> > array by MAX_NR_ZONES and place "#ifdef" to right place.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  include/linux/mmzone.h | 2 +-
> >  mm/page_alloc.c        | 7 ++++---
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index d572b78..e3f39af 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -877,7 +877,7 @@ int min_free_kbytes_sysctl_handler(struct ctl_table *, int,
> >  					void __user *, size_t *, loff_t *);
> >  int watermark_scale_factor_sysctl_handler(struct ctl_table *, int,
> >  					void __user *, size_t *, loff_t *);
> > -extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1];
> > +extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES];
> >  int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int,
> >  					void __user *, size_t *, loff_t *);
> >  int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 4f7d5d7..a8310de 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -198,17 +198,18 @@ static void __free_pages_ok(struct page *page, unsigned int order);
> >   * TBD: should special case ZONE_DMA32 machines here - in those we normally
> >   * don't need any ZONE_NORMAL reservation
> >   */
> > -int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
> > +int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES] = {
> >  #ifdef CONFIG_ZONE_DMA
> >  	 256,
> >  #endif
> >  #ifdef CONFIG_ZONE_DMA32
> >  	 256,
> >  #endif
> > -#ifdef CONFIG_HIGHMEM
> >  	 32,
> > +#ifdef CONFIG_HIGHMEM
> > +	 INT_MAX,
> >  #endif
> > -	 32,
> > +	 INT_MAX,
> >  };
> >
> >  EXPORT_SYMBOL(totalram_pages);
> > -- 
> > 1.9.1
> 
> We can also do things like below to make it readable ?
> 
> #ifdef CONFIG_ZONE_DMA
> 	[ZONE_DMA] = 256,
> #endif

It looks more readable! I will change it.

> 
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

Thanks!