Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 14038302 authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
Browse files

fs, proc: unconditional cond_resched when reading smaps 

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.

Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1708211405520.131071@chino.kir.corp.google.com


Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 855d9765

fs/proc/task_mmu.c

+3 −2
Original line number Diff line number Diff line
@@ -611,11 +611,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, 
		if (pmd_present(*pmd))

			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
@@ -625,6 +625,7 @@ 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;

}