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[2003:cb:c702:6300:c44f:789a:59b5:91e9]) by smtp.gmail.com with ESMTPSA id bh21-20020a05600c3d1500b003a2d6c623f3sm1954808wmb.19.2022.07.08.04.40.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Jul 2022 04:40:33 -0700 (PDT) Message-ID: Date: Fri, 8 Jul 2022 13:40:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] x86/mm/tlb: ignore f->new_tlb_gen when zero To: Nadav Amit , linux-kernel@vger.kernel.org, Hugh Dickins , Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , x86@kernel.org, Linux MM , Nadav Amit , Dave Hansen , Peter Zijlstra , Andy Lutomirski References: <20220708003053.158480-1-namit@vmware.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220708003053.158480-1-namit@vmware.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657280437; a=rsa-sha256; cv=none; b=opkpI+Lns95ANvTIAlMrq75K03UkhV3wHHmIh1M62IV6bvktOV0eWVJ36UhjhmP+kF+vAi zTHvlnTR+SIDbDj0BoNQGin1dcpcI6rqgFOdD1230YgC5q7K0foYGF0O8tTHOOsYc4tGSi MTfuHuLzJMRPRRTXnbyBhY3DKSl9Ksg= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ctTYfaJZ; spf=none (imf07.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657280437; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wXQSLj7N0OPVrbql97FSOxJxi1gzgZ5rqCr//cm7fcI=; b=nkDYScM/+tscJxPoc9Rl7bBFWEMPjl24ccj83ApvBm3q3m7Tawn6UlQrqjY9MePJCnhmtg 5cd3M8ksteZT60ReQ7JTvxv+MXCTZWzAqKHNvjFngeFtT19A7mzJUkAklYP2fn691BK1K2 v3FvN35Ah9UjxTj5SHbNntnS7LEDnqE= X-Rspamd-Server: rspam08 X-Rspam-User: Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ctTYfaJZ; spf=none (imf07.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: 7coumi3r9gpi3ddn6qc8xwb5zwad8yxo X-Rspamd-Queue-Id: D6C6740016 X-HE-Tag: 1657280436-773275 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 08.07.22 02:30, Nadav Amit wrote: > From: Nadav Amit > > Commit aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when > possible") introduced an optimization of skipping the flush if the TLB > generation that is flushed (as provided in flush_tlb_info) was already > flushed. > > However, arch_tlbbatch_flush() does not provide any generation in > flush_tlb_info. As a result, try_to_unmap_one() would not perform any > TLB flushes. > > Fix it by checking whether f->new_tlb_gen is nonzero. Zero value is > anyhow is an invalid generation value. > > In addition, add the missing unlikely() and jump to get tracing right. > > Fixes: aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when possible") > Reported-by: Hugh Dickins > Cc: Dave Hansen > Cc: Peter Zijlstra (Intel) > Cc: Andy Lutomirski > Signed-off-by: Nadav Amit > --- > arch/x86/mm/tlb.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index d9314cc8b81f..d81b4084bb8a 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -771,14 +771,14 @@ static void flush_tlb_func(void *info) > return; > } > > - if (f->new_tlb_gen <= local_tlb_gen) { > + if (unlikely(f->new_tlb_gen != 0 && f->new_tlb_gen <= local_tlb_gen)) { > /* > * The TLB is already up to date in respect to f->new_tlb_gen. > * While the core might be still behind mm_tlb_gen, checking > * mm_tlb_gen unnecessarily would have negative caching effects > * so avoid it. > */ > - return; > + goto done; Does this affect the performance numbers from aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when possible")? -- Thanks, David / dhildenb