Messages in this thread | | | Date | Tue, 22 Aug 2017 00:41:50 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [patch] fs, proc: unconditional cond_resched when reading smaps |
| |
On Mon, Aug 21, 2017 at 02:06:45PM -0700, David Rientjes wrote: > 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@google.com> > --- > 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; > }
Maybe just call cond_resched() at the beginning of the function and don't bother with gotos?
-- Kirill A. Shutemov
| |