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[70.30.145.63]) by smtp.gmail.com with ESMTPSA id w25-20020ac86b19000000b003b63c08a888sm4734754qts.4.2023.01.19.14.37.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 14:37:32 -0800 (PST) Date: Thu, 19 Jan 2023 17:37:31 -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: [PATCH 35/46] hugetlb: add MADV_COLLAPSE for hugetlb Message-ID: References: <20230105101844.1893104-1-jthoughton@google.com> <20230105101844.1893104-36-jthoughton@google.com> MIME-Version: 1.0 In-Reply-To: <20230105101844.1893104-36-jthoughton@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EA0F5180016 X-Stat-Signature: ztikktkya6bp8xt6154ush551faqy9hi X-HE-Tag: 1674167855-639069 X-HE-Meta: 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 gAN5ucyh Ld0myYvZX4OdFZofOy7+6xuoH8hT2QN1O8YTP0k7Rp7ik1Oj3DDQwaTNUFF4opAt2ZBmuzulSo4ow33B/+8MELy94aKkLrn+lzAwJuSKBtgH7Vngj3/CAroPk9KdQUn6PXNxEUocRcgqofVQAmtAYa3k/N2bdSEN1xDoHKLX36IssPL36GgaTFX4oFzsP82OyItl/0WplzjEizm2P8V1gY2B9PS0zRUgobw9Aso2dpWW3/4jrlUczu6UFUweOdpBHBL2CFC+nn6xjg3EUWW7WNvGKm+yHVtSzzVN9KLeCaNll5xQVoG6GmX81GOFJESSupZz+QHl0kGaN/DWVgs44v5IuBaAui71oSkw2Zr5UShYO5DKby6qC428yAkwy9nm/qfjktOCFehnqhG7CuFEm66jtkjqMfBx9bXOCsK/ghbTKfrk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000095, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jan 05, 2023 at 10:18:33AM +0000, James Houghton wrote: > + /* > + * Grab the VMA lock and mapping sem for writing. This will prevent > + * concurrent high-granularity page table walks, so that we can safely > + * collapse and free page tables. > + * > + * This is the same locking that huge_pmd_unshare requires. > + */ > + hugetlb_vma_lock_write(vma); > + i_mmap_lock_write(vma->vm_file->f_mapping); One thing I just noticed - do we need the mmap write lock here? I don't quickly see what stops another thread from having the mmap read and walking upon the pgtables being collapsed. Thanks, -- Peter Xu