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AJvYcCV3NYmMzXuAGNDZ/rpIrlD4QofW96443nOHGvbWgvVEvWul2UODeQiTrnUUO4n0VBr5WdoyqHxunw==@kvack.org X-Gm-Message-State: AOJu0Yx6rID/Ec925d1Ufeo2u265M7YB4u+VY3UvEcWMJeLJARxnz5vJ gZVnNW8I4fR0r7GUjUwznRTygEQjwKv/vCrxaV1wEXJnHK0FjEazY8V0ZL6zwNM4DUv2Szdg2o4 Gf8zMPKcDYFBr85ywhsS7dlhEEJBKe8qm2jaAFJvAOA== X-Gm-Gg: AY/fxX5qoxobGw+sCCmSeSE5cEEnlDUfjV+32E38+zzI9AVtprkSVa02kLiOyd0d+5B DFDGfRtBm5l+M4ecDkEvf84AJjsUpz+pOBZxq8idjeAkVtjcZ53VHKv+tn04OB2ehQbKBJRWoRJ m78yPuKKhq87sRiNx9lxUngVMVdDJWIvVVMSSnyz2eIBv+N1oqFVcGvIBgWXW15icJugAqYq0ep iuaPNQIzpJpKalCEXOtV2IegrI5otEY+Hap6ccRMzmasP22m8rrg6INNDxKhRslceZZ6hKWoHS/ 9ZNGAve42Zwyui51u/r7ZH50qA== X-Google-Smtp-Source: AGHT+IEIcVeNdEfJcm9VqUd+E8mWDB9V1hWp7w0giAMhCSKTNrPtcUlGUPRtf1huaKH0b5X5NkhBYKjrvd/UfQeEqC0= X-Received: by 2002:a05:6402:13c9:b0:64d:1294:42e8 with SMTP id 4fb4d7f45d1cf-64d12944806mr12214712a12.6.1766512781369; Tue, 23 Dec 2025 09:59:41 -0800 (PST) MIME-Version: 1.0 References: <20251206230222.853493-1-pratyush@kernel.org> <20251206230222.853493-2-pratyush@kernel.org> In-Reply-To: <20251206230222.853493-2-pratyush@kernel.org> From: Pasha Tatashin Date: Tue, 23 Dec 2025 12:59:05 -0500 X-Gm-Features: AQt7F2r0cpQB_ObkQOTsEIIl1kaIhEMZ8gs8RNljcXCPywOe6jERbxst1hl_vY8 Message-ID: Subject: Re: [RFC PATCH 01/10] kho: drop restriction on maximum page order To: Pratyush Yadav Cc: Mike Rapoport , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Muchun Song , Oscar Salvador , Alexander Graf , David Matlack , David Rientjes , Jason Gunthorpe , Samiullah Khawaja , Vipin Sharma , Zhu Yanjun , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, kexec@lists.infradead.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: EC20E80008 X-Stat-Signature: q5mwarpu8n9dr3boscapxjixf77rf7dw X-HE-Tag: 1766512782-236584 X-HE-Meta: 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 O/ipgGMF 9m3UP9jsc2eQN9AhjEuHZ5Zns9mI0AWzQjiHH1MqaMEx0uNyplXSqUMJdum9g5mm3caS8RVF/fd674H2gX3/x33PXMeDyn/evytED82YX1bDcvuPlkYJmQ9EuR75bq08Hv9/9mHklQYT5lNG4l25dltMJSdqHPLBY0Motk0oxhkfSCD8Da56qYCdTmcLvgtNn+B3/2rGDNrfEqc9e1TbXPhxWvw== 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: List-Subscribe: List-Unsubscribe: On Sat, Dec 6, 2025 at 6:03=E2=80=AFPM Pratyush Yadav = wrote: > > KHO currently restricts the maximum order of a restored page to the > maximum order supported by the buddy allocator. While this works fine > for much of the data passed across kexec, it is possible to have pages > larger than MAX_PAGE_ORDER. > > For one, it is possible to get a larger order when using > kho_preserve_pages() if the number of pages is large enough, since it > tries to combine multiple aligned 0-order preservations into one higher > order preservation. > > For another, upcoming support for hugepages can have gigantic hugepages > being preserved over KHO. > > There is no real reason for this limit. The KHO preservation machinery > can handle any page order. Remove this artificial restriction on max > page order. Before removing this restriction, please also add a patch that makes sure that the calculated order does not intermix memory from different topologies. I suspect we need something like this in kho_preserve_pages(): order =3D min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); /* Reduce order if the block spans across NUMA nodes. */ while (order > 0) { size_pfn =3D 1UL << order; if (pfn_to_nid(pfn) =3D=3D pfn_to_nid(pfn + size_pfn - 1)) break; order--; } Pasha