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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id x16sm2667189ooj.1.2021.08.08.21.29.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Aug 2021 21:29:32 -0700 (PDT) Date: Sun, 8 Aug 2021 21:29:29 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Matthew Wilcox cc: Hugh Dickins , Zi Yan , Vlastimil Babka , David Hildenbrand , linux-mm@kvack.org, "Kirill A . Shutemov" , Mike Kravetz , Michal Hocko , John Hubbard , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter. In-Reply-To: Message-ID: References: <20210805190253.2795604-1-zi.yan@sent.com> <0d374eed-cc52-a656-b338-1156782bdf7e@suse.cz> <6ae6cd92-3ff4-7ed3-b337-a4dfe33da1c@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=ugbfYuMF; spf=pass (imf25.hostedemail.com: domain of hughd@google.com designates 209.85.167.179 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C9FDDB00AB8A X-Stat-Signature: rktc3bcnrfa3z38qrkrzroynoi4zzkfg X-HE-Tag: 1628483373-701509 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, 7 Aug 2021, Matthew Wilcox wrote: > > I am, however, of the opinion that 2MB pages give us so much trouble > because they're so very special. Few people exercise those code paths and > it's easy to break them without noticing. This is partly why I want to > do arbitrary-order pages. If everybody is running with compound pages > all the time, we'll see the corner cases often, and people other than > Hugh, Kirill and Mike will be able to work on them. I don't entirely agree. I'm all for your use of compound pages in page cache, but don't think its problems are representative of the problems in aiming for a PMD (or PUD) bar, with the weird page table transitions we expect of "THP" there. I haven't checked: is your use of compound pages in page cache still limited to the HAVE_ARCH_TRANSPARENT_HUGEPAGE architectures? When the others could just as well use compound pages in page cache too. Hugh