Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request
From: Vlastimil Babka <hidden>
Date: 2017-08-24 09:42:03
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On 08/24/2017 07:45 AM, js1304@gmail.com wrote:
From: Joonsoo Kim <redacted> 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. Reviewed-by: Aneesh Kumar K.V <redacted> Acked-by: Vlastimil Babka <redacted>
Looks like I did that almost year ago, so definitely had to refresh my memory now :) Anyway now I looked more thoroughly and noticed that this change leaks into the reported sysctl. On a 64bit system with ZONE_MOVABLE: before the patch: vm.lowmem_reserve_ratio = 256 256 32 after the patch: vm.lowmem_reserve_ratio = 256 256 32 2147483647 So if we indeed remove HIGHMEM from protection (c.f. Michal's mail), we should do that differently than with the INT_MAX trick, IMHO.
quoted hunk ↗ jump to hunk
Signed-off-by: Joonsoo Kim <redacted> --- include/linux/mmzone.h | 2 +- mm/page_alloc.c | 11 ++++++----- 2 files changed, 7 insertions(+), 6 deletions(-)diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index e7e92c8..e5f134b 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h@@ -882,7 +882,7 @@ 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 90b1996..6faa53d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c@@ -202,17 +202,18 @@ 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, + [ZONE_DMA] = 256, #endif #ifdef CONFIG_ZONE_DMA32 - 256, + [ZONE_DMA32] = 256, #endif + [ZONE_NORMAL] = 32, #ifdef CONFIG_HIGHMEM - 32, + [ZONE_HIGHMEM] = INT_MAX, #endif - 32, + [ZONE_MOVABLE] = INT_MAX, }; EXPORT_SYMBOL(totalram_pages);
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