Re: [PATCH] mm/min_free_kbytes: modify min_free_kbytes calculation rules

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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)




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