linux-kernel - [PATCH] mm: make mem_map allocation continuous.

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Message-ID: <86802c440803102322i74333718h60de0da329b139c8@mail.gmail.com>
Date:	Mon, 10 Mar 2008 23:22:47 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Christoph Lameter" <clameter@....com>
Cc:	"kernel list" <linux-kernel@...r.kernel.org>
Subject: [PATCH] mm: make mem_map allocation continuous.

[PATCH] mm: make mem_map allocation continuous.

vmemmap allocation current got
 [ffffe20000000000-ffffe200001fffff] PMD ->ffff810001400000 on node 0
 [ffffe20000200000-ffffe200003fffff] PMD ->ffff810001800000 on node 0
 [ffffe20000400000-ffffe200005fffff] PMD ->ffff810001c00000 on node 0
 [ffffe20000600000-ffffe200007fffff] PMD ->ffff810002000000 on node 0
 [ffffe20000800000-ffffe200009fffff] PMD ->ffff810002400000 on node 0
...

there is 2M hole between them.

the rootcause is that usemap (24 bytes) will be allocated after every 2M
mem_map. and it will push next vmemmap (2M) to next align (2M).

solution:
try to allocate mem_map continously.

after patch, will get
 [ffffe20000000000-ffffe200001fffff] PMD ->ffff810001400000 on node 0
 [ffffe20000200000-ffffe200003fffff] PMD ->ffff810001600000 on node 0
 [ffffe20000400000-ffffe200005fffff] PMD ->ffff810001800000 on node 0
 [ffffe20000600000-ffffe200007fffff] PMD ->ffff810001a00000 on node 0
 [ffffe20000800000-ffffe200009fffff] PMD ->ffff810001c00000 on node 0
...
and usemap will share in page because of they are allocated continuously too.
sparse_early_usemap_alloc: usemap = ffff810024e00000 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00080 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00100 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00180 size = 24
...

so we make the bootmem allocation more compact and use less memory for usemap.

Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>

View attachment "vmemmap_1.patch" of type "text/x-patch" (1630 bytes)