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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 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221021163703.3218176-7-jthoughton@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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