Re: [PATCH] mm/min_free_kbytes: modify min_free_kbytes calculation rules
From: liuq
Date: Mon Jun 19 2023 - 08:44:33 EST
在 2023/6/19 11:25, Huang, Ying 写道:
Added Mel and Vlastimil.
liuq <liuq131@xxxxxxxxxxxxxxx> writes:
The current calculation of min_free_kbytes only uses ZONE_DMA and
ZONE_NORMAL pages,but the ZONE_MOVABLE zone->_watermark[WMARK_MIN]
will also divide part of min_free_kbytes.This will cause the min
watermark of ZONE_NORMAL to be too small in the presence of ZONE_MOVEABLE.
This seems like a real problem per my understanding. Can you show the
contents of /proc/zoneinfo on a problem system?
But, per my understanding, min_free_kbytes are used for __GFP_HIGH and
PF_MEMALLOC allocations. While ZONE_MOVABLE will not be used for them
usually. So I think we should treat ZONE_MOVABLE as ZONE_HIGHMEM in
__setup_per_zone_wmarks().
Best Regards,
Huang, Ying
On my testing machine with 16GB of memory (transparent hugepage is
turned off by default), when movable zone is not configured,
min_free_kbytes is 15806 (15806*15806/16=15614352kbytes, approximatel
y 16G).
The detailed info is as follows:
[root@lq-workstation ~]# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-6.2.0-rc7-00018-g0983f6bf2bfc-dirty
root=/dev/mapper/ctyunos00-root ro resume=/dev/mapper/ctyunos00-swap
rd.lvm.lv=ctyunos00/root rd.lvm.lv=ctyunos00/swap crashkernel=512M
[root@lq-workstation ~]# cat /proc/zoneinfo |grep -A 5 min
min 3
low 6
high 9
spanned 4095
present 3998
managed 3840
--
min 328
low 652
high 976
spanned 1044480
present 478802
managed 330969
--
min 3618
low 7193
high 10768
spanned 3655680
present 3655680
managed 3575787
--
min 0
low 0
high 0
spanned 0
present 0
managed 0
[root@lq-workstation ~]# cat /proc/sys/vm/min_free_kbytes
15806
If movablecore=12G is configured, at this time, min_free_kbytes is 7326
(7326 * 7326/16=3354392, approximately 16G-12G)
The detailed info is as follows:
[root@lq-workstation ~]# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-6.2.0-rc7-00018-g0983f6bf2bfc-dirty
root=/dev/mapper/ctyunos00-root ro resume=/dev/mapper/ctyunos00-swap
rd.lvm.lv=ctyunos00/root rd.lvm.lv=ctyunos00/swap crashkernel=512M
movablecore=12G
[root@lq-workstation ~]# cat /proc/zoneinfo |grep -A 5 min
min 1
low 4
high 7
spanned 4095
present 3998
managed 3840
--
min 152
low 476
high 800
spanned 1044480
present 478802
managed 330969
--
min 239
low 748
high 1257
spanned 509952
present 509952
managed 509952
--
min 1437
low 4502
high 7567
spanned 3145728
present 3145728
managed 3065833
[root@lq-workstation ~]# cat /proc/sys/vm/min_free_kbytes
7326
After this patch is added, the configuration of the movable zone no
longer affects the size of the min_free_kbytes, which is only affected
by the size of the available memory.
Signed-off-by: liuq <liuq131@xxxxxxxxxxxxxxx>
---
include/linux/mm.h | 1 +
mm/khugepaged.c | 2 +-
mm/page_alloc.c | 15 ++++++++++++++-
3 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index cf3d0d673f6b..1f91d035bcaf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -863,6 +863,7 @@ void split_page(struct page *page, unsigned int order);
void folio_copy(struct folio *dst, struct folio *src);
unsigned long nr_free_buffer_pages(void);
+unsigned long nr_free_pagecache_pages(void);
/*
* Compound pages have a destructor function. Provide a
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 16be62d493cd..6632264b951c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2342,7 +2342,7 @@ static void set_recommended_min_free_kbytes(void)
/* don't ever allow to reserve more than 5% of the lowmem */
recommended_min = min(recommended_min,
- (unsigned long) nr_free_buffer_pages() / 20);
+ (unsigned long) nr_free_pagecache_pages() / 20);
recommended_min <<= (PAGE_SHIFT-10);
if (recommended_min > min_free_kbytes) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3df0485..489b564526dd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5775,6 +5775,19 @@ unsigned long nr_free_buffer_pages(void)
}
EXPORT_SYMBOL_GPL(nr_free_buffer_pages);
+/**
+ * nr_free_pagecache_pages - count number of pages beyond high watermark
+ *
+ * nr_free_pagecache_pages() counts the number of pages which are beyond the
+ * high watermark within all zones.
+ *
+ * Return: number of pages beyond high watermark within all zones.
+ */
+unsigned long nr_free_pagecache_pages(void)
+{
+ return nr_free_zone_pages(gfp_zone(GFP_HIGHUSER_MOVABLE));
+}
+
static inline void show_node(struct zone *zone)
{
if (IS_ENABLED(CONFIG_NUMA))
@@ -8651,7 +8664,7 @@ void calculate_min_free_kbytes(void)
unsigned long lowmem_kbytes;
int new_min_free_kbytes;
- lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);
+ lowmem_kbytes = nr_free_pagecache_pages() * (PAGE_SIZE >> 10);
new_min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
if (new_min_free_kbytes > user_min_free_kbytes)