linux-kernel - Re: [PATCH] mm/page_alloc: Clean up check_for

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Message-ID: <20180831122401.GA2123@techadventures.net>
Date:   Fri, 31 Aug 2018 14:24:01 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH] mm/page_alloc: Clean up check_for_memory

On Thu, Aug 30, 2018 at 01:55:29AM +0000, Pasha Tatashin wrote:
> I would re-write the above function like this:
> static void check_for_memory(pg_data_t *pgdat, int nid)
> {
>         enum zone_type zone_type;
> 
>         for (zone_type = 0; zone_type < ZONE_MOVABLE; zone_type++) {
>                 if (populated_zone(&pgdat->node_zones[zone_type])) { 
>                         node_set_state(nid, zone_type <= ZONE_NORMAL ?
>                                        N_NORMAL_MEMORY: N_HIGH_MEMORY);
>                         break;
>                 }
>         }
> }

Hi Pavel,

the above would not work fine.
You set either N_NORMAL_MEMORY or N_HIGH_MEMORY, but a node can have both
types of memory at the same time (on CONFIG_HIGHMEM systems).

N_HIGH_MEMORY stands for regular or high memory
while N_NORMAL_MEMORY stands only for regular memory,
that is why we set it only in case the zone is <= ZONE_NORMAL.

> zone_type <= ZONE_MOVABLE - 1
> is the same as:
> zone_type < ZONE_MOVABLE

This makes sense.

-- 
Oscar Salvador
SUSE L3