If there are large numbers of hugepages to iterate while reading
/proc/pid/smaps, the page walk never does cond_resched(). On archs
without split pmd locks, there can be significant and observable
contention on mm->page_table_lock which cause lengthy delays without
rescheduling.
Always reschedule in smaps_pte_range() if necessary since the pagewalk
iteration can be expensive.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
fs/proc/task_mmu.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -599,11 +599,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
if (ptl) {
smaps_pmd_entry(pmd, addr, walk);
spin_unlock(ptl);
- return 0;
+ goto out;
}
if (pmd_trans_unstable(pmd))
- return 0;
+ goto out;
/*
* The mmap_sem held all the way back in m_start() is what
* keeps khugepaged out of here and from collapsing things
@@ -613,6 +613,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
for (; addr != end; pte++, addr += PAGE_SIZE)
smaps_pte_entry(pte, addr, walk);
pte_unmap_unlock(pte - 1, ptl);
+out:
cond_resched();
return 0;
}
--
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