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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id u19-20020a05620a0c5300b006fa84082b6dsm1858982qki.128.2022.11.30.13.01.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Nov 2022 13:01:05 -0800 (PST) Date: Wed, 30 Nov 2022 16:01:04 -0500 From: Peter Xu To: James Houghton Cc: Mike Kravetz , Muchun Song , David Hildenbrand , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 06/47] hugetlb: extend vma lock for shared vmas Message-ID: References: <20221021163703.3218176-1-jthoughton@google.com> <20221021163703.3218176-7-jthoughton@google.com> MIME-Version: 1.0 In-Reply-To: <20221021163703.3218176-7-jthoughton@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669842072; a=rsa-sha256; cv=none; b=Kmkg74O12iSidPMq/Olb/+A+9GHGZ7Eh0ncrgERo8UdGNM+MjUB3OK6pUWihZnogtHWnDu 3TU/tTW3X+ToC7iargccHjucB3lYd7+znfF9qC4Q/vHp7j0qOwR1L0+3JcVdvkEjPYZmws AF81BL9xmsQTKFn6oyGRhbsKj4jUCkI= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=P0PC91QI; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669842072; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=L42rLHtFBFKGLDIxtx1wN/+Aa4flR65WbTjaBq4HhSM=; b=380MtlUEUMVcjHnC7GKGzO57v/kZUv7dVImaJDitkUowqG5BQtJPJzIY+sWZPJ3y5Xg2AV 4yOxlhXgFlVu1h41Si2ymlK7kH+IUAV6fOl6EFa3TvjBiXv2R3xZ7L12Z2AnWBZ/FiFaG2 8wiu+KtpH/E+YarKYIIQp2YArpERmpY= X-Rspamd-Queue-Id: 0D72B40018 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=P0PC91QI; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: 4i5jtyndiu1rkeji14mxkqmw5ym7ytuc X-HE-Tag: 1669842071-487023 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 Fri, Oct 21, 2022 at 04:36:22PM +0000, James Houghton wrote: > This allows us to add more data into the shared structure, which we will > use to store whether or not HGM is enabled for this VMA or not, as HGM > is only available for shared mappings. > > It may be better to include HGM as a VMA flag instead of extending the > VMA lock structure. > > Signed-off-by: James Houghton > --- > include/linux/hugetlb.h | 4 +++ > mm/hugetlb.c | 65 +++++++++++++++++++++-------------------- > 2 files changed, 37 insertions(+), 32 deletions(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index a899bc76d677..534958499ac4 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -121,6 +121,10 @@ struct hugetlb_vma_lock { > struct vm_area_struct *vma; > }; > > +struct hugetlb_shared_vma_data { > + struct hugetlb_vma_lock vma_lock; > +}; How about add a comment above hugetlb_vma_lock showing how it should be used correctly? We lacked documents on the lock for pmd sharing protections, now if to reuse the same lock for HGM pgtables I think some doc will definitely help. To summarize, I think so far it means: - Read lock needed when one wants to stablize VM_SHARED pgtables (covers both pmd shared pgtables or hgm low-level pgtables) - Write lock needed when one wants to release VM_SHARED pgtable pages (covers both pmd unshare or releasing hgm low-level pgtables) Or something like that. -- Peter Xu