linux-kernel - [PATCH] mm: release the spinlock on zap_pte

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Message-Id: <20190729071037.241581-1-minchan@kernel.org>
Date:   Mon, 29 Jul 2019 16:10:37 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Minchan Kim <minchan@...nel.org>,
        Miguel de Dios <migueldedios@...gle.com>,
        Wei Wang <wvw@...gle.com>, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH] mm: release the spinlock on zap_pte_range

In our testing(carmera recording), Miguel and Wei found unmap_page_range
takes above 6ms with preemption disabled easily. When I see that, the
reason is it holds page table spinlock during entire 512 page operation
in a PMD. 6.2ms is never trivial for user experince if RT task couldn't
run in the time because it could make frame drop or glitch audio problem.

This patch adds preemption point like coyp_pte_range.

Reported-by: Miguel de Dios <migueldedios@...gle.com>
Reported-by: Wei Wang <wvw@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 mm/memory.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 2e796372927fd..bc3e0c5e4f89b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1007,6 +1007,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 				struct zap_details *details)
 {
 	struct mm_struct *mm = tlb->mm;
+	int progress = 0;
 	int force_flush = 0;
 	int rss[NR_MM_COUNTERS];
 	spinlock_t *ptl;
@@ -1022,7 +1023,16 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 	flush_tlb_batched_pending(mm);
 	arch_enter_lazy_mmu_mode();
 	do {
-		pte_t ptent = *pte;
+		pte_t ptent;
+
+		if (progress >= 32) {
+			progress = 0;
+			if (need_resched())
+				break;
+		}
+		progress += 8;
+
+		ptent = *pte;
 		if (pte_none(ptent))
 			continue;
 
@@ -1123,8 +1133,11 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 	if (force_flush) {
 		force_flush = 0;
 		tlb_flush_mmu(tlb);
-		if (addr != end)
-			goto again;
+	}
+
+	if (addr != end) {
+		progress = 0;
+		goto again;
 	}
 
 	return addr;
-- 
2.22.0.709.g102302147b-goog