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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. 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 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 08, 2021 at 09:29:29PM -0700, Hugh Dickins wrote: > 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. It is no longer gated by whether TRANSPARENT_HUGEPAGE is enabled or not. That's a relatively recent change, and I can't say that I've tested it. I'll give it a try today on a PA-RISC system I've booted recently. One of the followup pieces of work that I hope somebody other than myself will undertake is using 64KB PTEs on a 4KB PAGE_SIZE ARM/POWER machine if the stars align.