Possible partial miss in pages needed for zone's memory map?
Subsystems (2)
Hi,
I stumbled over the following in the zone initialization code. Please let me know if I overlooked something here.
---
From: Johannes Weiner <[email protected]>
Subject: [PATCH] Don't drop a partial page in a zone's memory map size
In a zone's present pages number, account for all pages occupied by the memory map, including a partial.
---
mm/page_alloc.c +2 -1
@@ -3378,7 +3378,8 @@ static void __paginginit free_area_init_* is used by this zone for memmap. This affects the watermark * and per-cpu initialisations */ - memmap_pages = (size *sizeof (struct page )) >>PAGE_SHIFT ; + memmap_pages = +PAGE_ALIGN (size *sizeof (struct page )) >>PAGE_SHIFT ;if (realsize >= memmap_pages) { realsize -= memmap_pages; printk(KERN_DEBUG
Andrew Morton
maintainerQuoted 5 lines · On Sat, 17 May 2008 14:19:15 +0200 Johannes Weiner <[email protected]> wrote:
Hi,
I stumbled over the following in the zone initialization code. Please let me know if I overlooked something here.
hm, no takers. Let's add linux-mm.
Quoted 13 lines
From: Johannes Weiner <[email protected]>
Subject: [PATCH] Don't drop a partial page in a zone's memory map sizeIn a zone's present pages number, account for all pages occupied by the memory map, including a partial.
Signed-off-by Johannes Weiner <[email protected]>---
mm/page_alloc.c static void __paginginit free_area_init_ · line 3385
Quoted 9 lines
mm/page_alloc.c +2
-1@@ -3378,7 +3378,8 @@ static void __paginginit free_area_init_* is used by this zone for memmap. This affects the watermark * and per-cpu initialisations */ - memmap_pages = (size *sizeof (struct page )) >>PAGE_SHIFT ; + memmap_pages = +PAGE_ALIGN (size *sizeof (struct page )) >>PAGE_SHIFT ;if (realsize >= memmap_pages) { realsize -= memmap_pages; printk(KERN_DEBUG
I looked in there for 30 seconds and collapsed in confusion over which variables are in which units.
Hint: never ever name a variable or a /proc file or your cat or anything else anything dimensionless like "size". It can always be replaced with something which communicates its units. zones_nrbytes, zholes_nrpages, etc.
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Quoted 20 lines · On Mon, 19 May 2008 23:19:37 -0700 Andrew Morton <[email protected]>…
Quoted 5 lines · On Sat, 17 May 2008 14:19:15 +0200 Johannes Weiner <[email protected]> wrote:
Hi,
I stumbled over the following in the zone initialization code. Please let me know if I overlooked something here.
hm, no takers. Let's add linux-mm.
Quoted 10 lines
From: Johannes Weiner <[email protected]>
Subject: [PATCH] Don't drop a partial page in a zone's memory map sizeIn a zone's present pages number, account for all pages occupied by the memory map, including a partial.
Signed-off-by Johannes Weiner <[email protected]>---
Quoted 16 lines
mm/page_alloc.c static void __paginginit free_area_init_ · line 3385
Quoted 12 lines
mm/page_alloc.c +2
-1@@ -3378,7 +3378,8 @@ static void __paginginit free_area_init_* is used by this zone for memmap. This affects the watermark * and per-cpu initialisations */ - memmap_pages = (size *sizeof (struct page )) >>PAGE_SHIFT ; + memmap_pages = +PAGE_ALIGN (size *sizeof (struct page )) >>PAGE_SHIFT ;if (realsize >= memmap_pages) { realsize -= memmap_pages; printk(KERN_DEBUGI looked in there for 30 seconds and collapsed in confusion over which variables are in which units.
Hmm, size * sizeof(struct page) is multiple of PAGE_SIZE in many case. Becasue "size" is always alinged to (1 << MAX_ORDER -1) (I believe...).
ex.) In x86 case,
(1 << (MAX_ORDER(11) - 1)) * 4 (sizeof(long)) = (1 << 12) = PAGE_SIZE.
But not sure on other archs with various params.
I think above fix is correct.
Thanks,
-Kame