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mm: vmscan: split khugepaged stats from direct reclaim stats

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Direct reclaim stats are useful for identifying a potential source for
application latency, as well as spotting issues with kswapd.  However,
khugepaged currently distorts the picture: as a kernel thread it doesn't
impose allocation latencies on userspace, and it explicitly opts out of
kswapd reclaim.  Its activity showing up in the direct reclaim stats is
misleading.  Counting it as kswapd reclaim could also cause confusion when
trying to understand actual kswapd behavior.

Break out khugepaged from the direct reclaim counters into new
pgsteal_khugepaged, pgdemote_khugepaged, pgscan_khugepaged counters.

Test with a huge executable (CONFIG_READ_ONLY_THP_FOR_FS):

pgsteal_kswapd 1342185
pgsteal_direct 0
pgsteal_khugepaged 3623
pgscan_kswapd 1345025
pgscan_direct 0
pgscan_khugepaged 3623

Link: https://lkml.kernel.org/r/20221026180133.377671-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Eric Bergen <ebergen@meta.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Johannes Weiner
2022-10-26 14:01:33 -04:00
committed by Andrew Morton
parent 1b01663875
commit 57e9cc50f4
7 changed files with 53 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/khugepaged.h
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@@ -15,6 +15,7 @@ extern void __khugepaged_exit(struct mm_struct *mm);
extern void khugepaged_enter_vma(struct vm_area_struct *vma,
unsigned long vm_flags);
extern void khugepaged_min_free_kbytes_update(void);
extern bool current_is_khugepaged(void);
#ifdef CONFIG_SHMEM
extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
bool install_pmd);
@@ -57,6 +58,11 @@ static inline int collapse_pte_mapped_thp(struct mm_struct *mm,
static inline void khugepaged_min_free_kbytes_update(void)
{
}
static inline bool current_is_khugepaged(void)
{
return false;
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif /* _LINUX_KHUGEPAGED_H */