linux-kernel - [PATCH 06/10] mm/page_alloc: Reduce duration that IRQs are disabled for VM counters

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Message-Id: <20210419141341.26047-7-mgorman@techsingularity.net>
Date:   Mon, 19 Apr 2021 15:13:37 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Linux-MM <linux-mm@...ck.org>,
        Linux-RT-Users <linux-rt-users@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 06/10] mm/page_alloc: Reduce duration that IRQs are disabled for VM counters

IRQs are left disabled for the zone and node VM event counters. This is
unnecessary as the affected counters are allowed to race for preemmption
and IRQs.

This patch reduces the scope of IRQs being disabled
via local_[lock|unlock]_irq on !PREEMPT_RT kernels. One
__mod_zone_freepage_state is still called with IRQs disabled. While this
could be moved out, it's not free on all architectures as some require
IRQs to be disabled for mod_zone_page_state on !PREEMPT_RT kernels.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cff0f1c98b28..295624fe293b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3474,11 +3474,11 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
 	pcp = this_cpu_ptr(zone->per_cpu_pageset);
 	list = &pcp->lists[migratetype];
 	page = __rmqueue_pcplist(zone,  migratetype, alloc_flags, pcp, list);
+	local_unlock_irqrestore(&pagesets.lock, flags);
 	if (page) {
 		__count_zid_vm_events(PGALLOC, page_zonenum(page), 1);
 		zone_statistics(preferred_zone, zone, 1);
 	}
-	local_unlock_irqrestore(&pagesets.lock, flags);
 	return page;
 }
 
@@ -3530,15 +3530,15 @@ struct page *rmqueue(struct zone *preferred_zone,
 		if (!page)
 			page = __rmqueue(zone, order, migratetype, alloc_flags);
 	} while (page && check_new_pages(page, order));
-	spin_unlock(&zone->lock);
 	if (!page)
 		goto failed;
+
 	__mod_zone_freepage_state(zone, -(1 << order),
 				  get_pcppage_migratetype(page));
+	spin_unlock_irqrestore(&zone->lock, flags);
 
 	__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
 	zone_statistics(preferred_zone, zone, 1);
-	local_irq_restore(flags);
 
 out:
 	/* Separate test+clear to avoid unnecessary atomics */
@@ -3551,7 +3551,7 @@ struct page *rmqueue(struct zone *preferred_zone,
 	return page;
 
 failed:
-	local_irq_restore(flags);
+	spin_unlock_irqrestore(&zone->lock, flags);
 	return NULL;
 }
 
@@ -5103,11 +5103,11 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 		nr_populated++;
 	}
 
+	local_unlock_irqrestore(&pagesets.lock, flags);
+
 	__count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
 	zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
 
-	local_unlock_irqrestore(&pagesets.lock, flags);
-
 	return nr_populated;
 
 failed_irq:
-- 
2.26.2