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@gmail.com writes:

quoted

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.

Signed-off-by: Joonsoo Kim <redacted>
---
 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 <redacted>

Thanks!

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