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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wAYuI-00000005rWi-2gai; Wed, 08 Apr 2026 19:49:46 +0000 Date: Wed, 8 Apr 2026 20:49:46 +0100 From: Matthew Wilcox To: Usama Arif Cc: Hugh Dickins , Andrew Morton , david@kernel.org, Lorenzo Stoakes , linux-mm@kvack.org, fvdl@google.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, maddy@linux.ibm.com, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, linux-s390@vger.kernel.org Subject: Re: [v3 00/24] mm: thp: lazy PTE page table allocation at PMD split time Message-ID: References: <20260327021403.214713-1-usama.arif@linux.dev> <6869b7f0-84e1-fb93-03f1-9442cdfe476b@google.com> <3f9e8e12-2d51-4f2a-ada1-994ed24df284@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3f9e8e12-2d51-4f2a-ada1-994ed24df284@linux.dev> X-Rspam-User: X-Stat-Signature: 6zybk54j1wqux8x6tr775igiudzpc1cm X-Rspamd-Queue-Id: 3061F12000E X-Rspamd-Server: rspam09 X-HE-Tag: 1775677793-671626 X-HE-Meta: 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 ucEGZx+U 7Uaz5ObZFkDG1lVgKa8CpR0vnGsdVcqpYXJT3KsYKjPSIkURLFmf8AONVni+Dm8A07u5sdCItnBX/ijY3pBYunWATXPM3mpfxH8KQnRmhtmZdoYQXEbZGXMlXBp1ZZKX0xI0tQ54UJBoiybeQWxerAaMByQIIDgDGT5VqVBBwl6bmwoOxkJvZzAH80YLEWr3UNnwdUB2Rmf9gq0suu+/Tj7TJUGbOHTjEQXdeY02SZhbt36NbCykiZ8WV/nd/uMdBQucO Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 08, 2026 at 04:06:29PM +0100, Usama Arif wrote: > On 06/04/2026 00:34, Hugh Dickins wrote: > > What would help a lot would be the implementation of swap entries > > at the PMD level. Whether that would help enough, I'm sceptical: > > I do think it's foolish to depend upon the availability of huge > > contiguous swap extents, whatever the recent improvements there; > > but it would at least be an arguable justification. > > > Thanks for pointing this out. I should have thought of this as I > have been thinking about fork a lot for 1G THP and for this series. > > I am working on trying to make PMD level swap entires work. I hope > to have a RFC soon. I think you may have missed Hugh's point a little bit. If we do support PMD-level swap entries, that means we have to be able to find contiguous space in the swap space for 512 entries. I don't know how hard that will be, but I can imagine it's not that easy.