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Sun, 02 Aug 2026 16:05:23 -0700 (PDT) Date: Sun, 2 Aug 2026 16:05:22 -0700 (PDT) From: David Rientjes To: Usama Arif cc: Andrew Morton , David Hildenbrand , Christoph Lameter , Vlastimil Babka , Mathieu Desnoyers , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/3] lib: test_vmstat: add synthetic benchmark for vm stats In-Reply-To: <20260801132038.2926647-1-usama.arif@linux.dev> Message-ID: References: <20260801132038.2926647-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Sat, 1 Aug 2026, Usama Arif wrote: > > diff --git a/lib/test_vmstat.c b/lib/test_vmstat.c > > new file mode 100644 > > index 000000000000..f63f439ab9d2 > > --- /dev/null > > +++ b/lib/test_vmstat.c > > @@ -0,0 +1,95 @@ > > +// SPDX-License-Identifier: GPL-2.0-or-later > > +/* > > + * Test module for in-kernel synthetic vm statistics performance. > > + * > > + * execute > > + * > > + * modprobe test_vmstat > > + * > > + * to run this test > > + * > > + * (C) 2009 Linux Foundation, Christoph Lameter > > + */ > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#define TEST_COUNT 10000 > > + > > +static int vmstat_test_init(void) > > +{ > > + unsigned int i; > > + cycles_t time1, time2, time; > > + int rem; > > + struct page *page = alloc_page(GFP_KERNEL); > > + > > Good to check page != NULL before using it below. > > > + pr_alert("VMstat testing\n"); > > + pr_alert("=====================\n"); > > + pr_alert("1. inc_zone_page_state() then dec_zone_page_state()\n"); > > + time1 = get_cycles(); > > + for (i = 0; i < TEST_COUNT; i++) > > + inc_zone_page_state(page, NR_FREE_CMA_PAGES); > > + > > + time2 = get_cycles(); > > + time = time2 - time1; > > + > > + pr_alert("%i times inc_zone_page_state() ", i); > > + time = div_u64_rem(time, TEST_COUNT, &rem); > > + pr_cont("-> %llu cycles ", (unsigned long long) time); > > + > > + time1 = get_cycles(); > > + for (i = 0; i < TEST_COUNT; i++) > > + __dec_zone_page_state(page, NR_FREE_CMA_PAGES); > > Why use inc_zone_page_state() but the __ variant for decrement? > > Checking the 2 functions, __dec_zone_page_state() might cause > problems if preemption is enabled? > Fixed both, thanks!