From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id D2D756B04F2 for ; Mon, 21 Aug 2017 17:41:53 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id b14so9087287wrd.11 for ; Mon, 21 Aug 2017 14:41:53 -0700 (PDT) Received: from mail-wr0-x236.google.com (mail-wr0-x236.google.com. [2a00:1450:400c:c0c::236]) by mx.google.com with ESMTPS id y43si1646035edd.48.2017.08.21.14.41.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 21 Aug 2017 14:41:52 -0700 (PDT) Received: by mail-wr0-x236.google.com with SMTP id z91so108004298wrc.4 for ; Mon, 21 Aug 2017 14:41:52 -0700 (PDT) Date: Tue, 22 Aug 2017 00:41:50 +0300 From: "Kirill A. Shutemov" Subject: Re: [patch] fs, proc: unconditional cond_resched when reading smaps Message-ID: <20170821214150.pgv3ulpicnacslak@node.shutemov.name> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Andrew Morton , Minchan Kim , Hugh Dickins , "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, linux-mm@kvack.org 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 > --- > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org