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Shutemov" , Yang Shi , Zi Yan , Matthew Wilcox , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Rientjes Subject: Re: [PATCH] mm: split thp synchronously on MADV_DONTNEED Message-ID: References: <20211120201230.920082-1-shakeelb@google.com> <25b36a5c-5bbd-5423-0c67-05cd6c1432a7@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 261A0508BB87 X-Stat-Signature: ebc7ct5k5f845ygi54zg94oxdjn4hrtk Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=XWkpyBbL; spf=none (imf05.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1637919587-75530 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, Nov 26, 2021 at 10:16:58AM +0100, David Hildenbrand wrote: > Would this really apply to MADV_DONTNEED on shmem, and would deferred > splitting apply on shmem? I'm constantly confused about shmem vs. anon, > but I would have assumed that shmem is fd-based and we wouldn't end up > in rmap_walk_anon. For shmem, the pagecache would contain the THP which > would stick around and deferred splits don't even apply. Good point.. when split on shmem we just clear pmd, so yeah I don't think we'll ever add it into the deferred list. > User space can trigger a split manually using some MADV hackery. But it > can only be used for the use case here, where we actually want to zap a > page. > > 1. MADV_FREE a single 4k page in the range. This will split the PMD->PTE > and the compound page. Seems to be a very implicit but working solution indeed. > 2. MADV_DONTNEED either the complete range or the single 4k page. Is this what this patch is working on? Thanks, -- Peter Xu