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 <[email protected]> --- 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; }
