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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id bs11-20020ac86f0b000000b0039cc82a319asm2545425qtb.76.2022.10.30.11.43.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Oct 2022 11:43:53 -0700 (PDT) Date: Sun, 30 Oct 2022 14:43:51 -0400 From: Peter Xu To: Nadav Amit , Mike Kravetz Cc: Mike Kravetz , Linux-MM , kernel list , Naoya Horiguchi , David Hildenbrand , Axel Rasmussen , Mina Almasry , Rik van Riel , Vlastimil Babka , Matthew Wilcox , Andrew Morton , Wei Chen , stable@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH v2] hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing Message-ID: References: <20221023025047.470646-1-mike.kravetz@oracle.com> <7048D2B5-5FA5-4F72-8FDC-A02411CFD71D@gmail.com> MIME-Version: 1.0 In-Reply-To: <7048D2B5-5FA5-4F72-8FDC-A02411CFD71D@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667155437; 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=f++yjA22gDYnyDkTxD8DX0hMfV9eCOWk5hFBUUA9MAI=; b=SIYWtVKuBkTg6cekgt28GuMaw3nitN0lejvmBKFte5WSTLYpX7tncn2cXEh0JFZPq9Z24o yoERr8EfphxU9PqR+ZKFXaiLbQEoZGyKK2kvOZQpCMAPGBrPCSyySD1wwZOe0vdzefb19m Ws2k2Svw9/n/B28KRSwghKFIP1nRewg= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=gwwH6Z06; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667155437; a=rsa-sha256; cv=none; b=kg6MqSokGep9wz0rsBYtqm7ArvXcYFUtJ4OfHmUYk5W1bsHGN4oLrjhHb8EQduaZ9dFDWf rPxCBY+yJmkz4pw3mNCoG5zxIVXqYYwmKcW3wrg83Ye9896r6Wx9yWFWHKsN1oi0XWtNXK EwhWyNrAd4/7JLwlnWXI0JED4Nu8JDY= X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 295BC20008 Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=gwwH6Z06; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf03.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com X-Stat-Signature: rjyyk8nn183ag3whmen1gqb9sfyusxb7 X-Rspam-User: X-HE-Tag: 1667155436-894751 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 Sat, Oct 29, 2022 at 05:54:44PM -0700, Nadav Amit wrote: > On Oct 29, 2022, at 5:15 PM, Mike Kravetz wrote: > > > zap_page_range is a bit confusing. It appears that the passed range can > > span multiple vmas. Otherwise, there would be no do while loop. Yet, there > > is only one mmu_notifier_range_init call specifying the passed vma. > > > > It appears all callers pass a range entirely within a single vma. > > > > The modifications above would work for a range within a single vma. However, > > things would be more complicated if the range can indeed span multiple vmas. > > For multiple vmas, we would need to check the first and last vmas for > > pmd sharing. > > > > Anyone know more about this seeming confusing behavior? Perhaps, range > > spanning multiple vmas was left over earlier code? > > I don’t have personal knowledge, but I noticed that it does not make much > sense, at least for MADV_DONTNEED. I tried to batch the TLB flushes across > VMAs for madvise’s. [1] The loop comes from 7e027b14d53e ("vm: simplify unmap_vmas() calling convention", 2012-05-06), where zap_page_range() was used to replace a call to unmap_vmas() because the patch wanted to eliminate the zap details pointer for unmap_vmas(), which makes sense. I didn't check the old code, but from what I can tell (and also as Mike pointed out) I don't think zap_page_range() in the lastest code base is ever used on multi-vma at all. Otherwise the mmu notifier is already broken - see mmu_notifier_range_init() where the vma pointer is also part of the notification. Perhaps we should just remove the loop? > > Need to get to it sometime. > > [1] https://lore.kernel.org/lkml/20210926161259.238054-7-namit@vmware.com/ > -- Peter Xu