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Tue, 16 May 2023 04:07:22 -0400 X-MC-Unique: N_FfV3yGM9a_z09cgAqLSQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1C83D878522; Tue, 16 May 2023 08:07:22 +0000 (UTC) Received: from localhost (ovpn-13-34.pek2.redhat.com [10.72.13.34]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EA61E40C6EC4; Tue, 16 May 2023 08:07:20 +0000 (UTC) Date: Tue, 16 May 2023 16:07:17 +0800 From: Baoquan He To: Thomas Gleixner Cc: Uladzislau Rezki , Andrew Morton , linux-mm@kvack.org, Christoph Hellwig , Lorenzo Stoakes , Peter Zijlstra , John Ogness , linux-arm-kernel@lists.infradead.org, Russell King , Mark Rutland , Marc Zyngier Subject: Re: Excessive TLB flush ranges Message-ID: References: <87a5y5a6kj.ffs@tglx> <87o7mk93tc.ffs@tglx> MIME-Version: 1.0 In-Reply-To: <87o7mk93tc.ffs@tglx> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Stat-Signature: 3h9r68wk9imuo9s4pq8s598suzhb37m6 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 0E4E81A0013 X-HE-Tag: 1684224446-601844 X-HE-Meta: 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 5ZkzGgv6 mcMb+iNoa6qf8lxb7tKrWokXByQoiRR/PJ8KJ7yJwZgwHkKVlidfXrDTYaDFQhut4cVPn3zRde9gxTGdgWwzFoMNrobT0Uv+FGM5dkU8X6T9VMgXc7ct4GbeniAmcDZ842Fj56+ZImzXzunr6gRQV+DOqxmj72O5pFurKIz4yWGq3J50= 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 05/16/23 at 08:40am, Thomas Gleixner wrote: > On Tue, May 16 2023 at 10:26, Baoquan He wrote: > > On 05/15/23 at 08:17pm, Uladzislau Rezki wrote: > >> For systems which lack a full TLB flush and to flush a long range is > >> a problem(it takes time), probably we can flush VA one by one. Because > >> currently we calculate a flush range [min:max] and that range includes > >> the space that might not be mapped at all. Like below: > > > > It's fine if we only calculate a flush range of [min:max] with VA. In > > vm_reset_perms(), it calculates the flush range with the impacted direct > > mapping range, then merge it with VA's range. That looks really strange > > and surprising. If the vm->pages[] are got from a lower part of physical > > memory, the final merged flush will span tremendous range. Wondering why > > we need merge the direct map range with VA range, then do flush. Not > > sure if I misunderstand it. > > So what happens on this BPF teardown is: > > The vfree(8k) ends up flushing 3 entries. The actual vmalloc part (2) and > one extra which is in the direct map. I haven't verified that yet, but I > assume it's the alias of one of the vmalloc'ed pages. It looks like the reason. As Uladzislau pointed out, ARCH-es may have full TLB flush, so won't get trouble from the merged flush in the calculated [min:max] way, e.g arm64 and x86's flush_tlb_kernel_range(). However, arm32 seems lacking the ability of full TLB flash. If agreed, I can make a draft patch to do the flush for direct map and VA seperately, see if it works.