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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qearR-000Bj5-PA; Fri, 08 Sep 2023 12:45:21 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 6D984300472; Fri, 8 Sep 2023 14:45:21 +0200 (CEST) Date: Fri, 8 Sep 2023 14:45:21 +0200 From: Peter Zijlstra To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org, tglx@linutronix.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH v2 9/9] x86/clear_huge_page: make clear_contig_region() preemptible Message-ID: <20230908124521.GD19320@noisy.programming.kicks-ass.net> References: <20230830184958.2333078-1-ankur.a.arora@oracle.com> <20230830184958.2333078-10-ankur.a.arora@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230830184958.2333078-10-ankur.a.arora@oracle.com> X-Rspamd-Queue-Id: 3933420031 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ro71u1maz37efwnziuzras6bmy3gyom9 X-HE-Tag: 1694177134-887156 X-HE-Meta: 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 kEhyki80 k6IHdeDWn73sEtQ+csHKsIzbAgQQpQtHnEXKpSVGnrRlV/Xl0io78fmSvC0okrFOKfhfBm5Crn8PiZp4htPChSwV3Ly0ViO0gpw33kgJLdcVkvkPQRVt31lv7Q6muNdkKJ+G5iHzCY/MuLMyaK2VxvDg4RH2rXx2BbgQc0Jl0A0PFWbuaTrAR/EXD/LjIojl9lrVgi9Ttz963/3U= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 30, 2023 at 11:49:58AM -0700, Ankur Arora wrote: > clear_contig_region() can be used for clearing regions as large as a > gigantic page. Allow preemption in irqentry_exit to make sure we don't > hold on to the CPU for an arbitrarily long period. It would be very nice to quantify the latency improvement here. At the very least perhaps mention how long a 2M or 1G clear takes (on you favourite machine) to illustrate why this is needed. > Signed-off-by: Ankur Arora > --- > arch/x86/mm/hugetlbpage.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c > index 0b9f7a6dad93..55d1d15ea618 100644 > --- a/arch/x86/mm/hugetlbpage.c > +++ b/arch/x86/mm/hugetlbpage.c > @@ -152,7 +152,12 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr, > #ifndef CONFIG_HIGHMEM > static void clear_contig_region(struct page *page, unsigned int npages) > { > + /* > + * We might be clearing a large region. Allow rescheduling. > + */ > + allow_resched(); > clear_pages(page_address(page), npages); > + disallow_resched(); > } Why is this in clear_contig_region() and not clear_pages() ? Any other clear_pages() user will have the same problems no?