linux-kernel - [PATCH 0/1 v2] Protect vmstats on PREEMPT

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Message-Id: <20210805160019.1137-1-mgorman@techsingularity.net>
Date:   Thu,  5 Aug 2021 17:00:18 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>, Linux-MM <linux-mm@...ck.org>,
        Linux-RT-Users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 0/1 v2] Protect vmstats on PREEMPT_RT

Changelog since v1
o Remove preempt_[en|dis]able_rt helper

When adding local_lock support to mm/page_alloc.c and reducing the overhead
of vmstats in general, I wondered how vmstats could be safe on PREEMPT_RT
as it partially relies on interrupts being disabled for the stats that
must be accurate for correctness. As it turns out, the preempt-rt tree
already encountered the same problem.

This series protects just the accurate counters. As Thomas expressed
concern that the preempt_enable_rt() helper could be abused, this
version open-codes the preemption with a comment explaining why it
is necessary.

This is specific to PREEMPT_RT which cannot be enabled on mainline yet
and should have no impact on !PREEMPT_RT kernels.

This patch replaces the following mmotm patches

o preempt-provide-preempt__nort-variants.patch
o mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch

-- 
2.31.1