mm: swap: Count successful large folio zswap stores in hugepage zswpo…

…ut stats.

Added a new MTHP_STAT_ZSWPOUT entry to the sysfs transparent_hugepage
stats so that successful large folio zswap stores can be accounted under
the per-order sysfs "zswpout" stats:

/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout

Other non-zswap swap device swap-out events will be counted under
the existing sysfs "swpout" stats:

/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/swpout

Also, added documentation for the newly added sysfs per-order hugepage
"zswpout" stats. The documentation clarifies that only non-zswap swapouts
will be accounted in the existing "swpout" stats.

Link: https://lkml.kernel.org/r/20241001053222.6944-8-kanchana.p.sridhar@intel.com
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Wajdi Feghali <wajdi.k.feghali@intel.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: "Zou, Nanhai" <nanhai.zou@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/admin-guide/mm/transhuge.rst

@@ -530,10 +530,14 @@ anon_fault_fallback_charge
  instead falls back to using huge pages with lower orders or
  small pages even though the allocation was successful.
 
-swpout
- is incremented every time a huge page is swapped out in one
+zswpout
+ is incremented every time a huge page is swapped out to zswap in one
  piece without splitting.
 
+swpout
+ is incremented every time a huge page is swapped out to a non-zswap
+ swap device in one piece without splitting.
+
 swpout_fallback
  is incremented if a huge page has to be split before swapout.
  Usually because failed to allocate some continuous swap space

include/linux/huge_mm.h

@@ -119,6 +119,7 @@ enum mthp_stat_item {
  MTHP_STAT_ANON_FAULT_ALLOC,
  MTHP_STAT_ANON_FAULT_FALLBACK,
  MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
+ MTHP_STAT_ZSWPOUT,
  MTHP_STAT_SWPOUT,
  MTHP_STAT_SWPOUT_FALLBACK,
  MTHP_STAT_SHMEM_ALLOC,

mm/huge_memory.c

@@ -611,6 +611,7 @@ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
 DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
 DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
+DEFINE_MTHP_STAT_ATTR(zswpout, MTHP_STAT_ZSWPOUT);
 DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
 DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
 #ifdef CONFIG_SHMEM
@@ -629,6 +630,7 @@ static struct attribute *anon_stats_attrs[] = {
  &anon_fault_fallback_attr.attr,
  &anon_fault_fallback_charge_attr.attr,
 #ifndef CONFIG_SHMEM
+ &zswpout_attr.attr,
  &swpout_attr.attr,
  &swpout_fallback_attr.attr,
 #endif
@@ -659,6 +661,7 @@ static struct attribute_group file_stats_attr_grp = {
 
 static struct attribute *any_stats_attrs[] = {
 #ifdef CONFIG_SHMEM
+ &zswpout_attr.attr,
  &swpout_attr.attr,
  &swpout_fallback_attr.attr,
 #endif

mm/page_io.c

@@ -269,6 +269,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
  swap_zeromap_folio_clear(folio);
  }
  if (zswap_store(folio)) {
+ count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
  folio_unlock(folio);
  return 0;
  }