linux-kernel - Re: [Question] Mlocked count will not be decreased

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Message-ID: <53778229-34ed-56a2-7f94-c8cd2f519de6@suse.cz>
Date:   Wed, 24 May 2017 12:42:21 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yisheng Xie <xieyisheng1@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, zhongjiang <zhongjiang@...wei.com>,
        Qiuxishi <qiuxishi@...wei.com>
Subject: Re: [Question] Mlocked count will not be decreased

On 05/24/2017 12:32 PM, Vlastimil Babka wrote:
> 
> Weird, I can reproduce the issue on my desktop's 4.11 distro kernel, but
> not in qemu and small kernel build, for some reason. So I couldn't test

Ah, Tetsuo's more aggressive testcase worked and I can confirm the fix.
However this would be slightly better, as it doesn't do the increment in
fastpath:

diff --git a/mm/mlock.c b/mm/mlock.c
index 0dd9ca18e19e..721679a2c1aa 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -286,7 +286,7 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 {
        int i;
        int nr = pagevec_count(pvec);
-       int delta_munlocked;
+       int delta_munlocked = -nr;
        struct pagevec pvec_putback;
        int pgrescued = 0;
 
@@ -306,6 +306,8 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
                                continue;
                        else
                                __munlock_isolation_failed(page);
+               } else {
+                       delta_munlocked++;
                }
 
                /*
@@ -317,7 +319,6 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
                pagevec_add(&pvec_putback, pvec->pages[i]);
                pvec->pages[i] = NULL;
        }
-       delta_munlocked = -nr + pagevec_count(&pvec_putback);
        __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
        spin_unlock_irq(zone_lru_lock(zone));