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Thu, 4 Jun 2026 19:33:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 10u7OAnTIWo3EwAAD6G6ig (envelope-from ); Thu, 04 Jun 2026 19:33:29 +0000 Date: Thu, 4 Jun 2026 20:33:23 +0100 From: Pedro Falcato To: Usama Arif Cc: Andrew Morton , david@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org, r@hev.cc, jack@suse.cz, Andrew Donnellan , apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, brauner@kernel.org, catalin.marinas@arm.com, dev.jain@arm.com, kees@kernel.org, kevin.brodsky@arm.com, lance.yang@linux.dev, "Liam R. Howlett" , linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, npache@redhat.com, pasha.tatashin@soleen.com, rmclure@linux.ibm.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, Al Viro , ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com Subject: Re: [PATCH v7 2/2] mm: use mapping_max_folio_order() for force_thp_readahead order Message-ID: References: <20260601102205.3985788-1-usama.arif@linux.dev> <20260601102205.3985788-3-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260601102205.3985788-3-usama.arif@linux.dev> X-Rspamd-Queue-Id: 4FA64C0012 X-Rspam-User: X-Stat-Signature: b63ce4xfg7p3cyj1beqbntkr4e4afx8c X-Rspamd-Server: rspam08 X-HE-Tag: 1780601614-987486 X-HE-Meta: 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 RP0xu7eb 46VIAXlTqLGwq+LJqXRy24pg6Gaw2V5m8ljIV+Cm4cyaErXR2g4a9kHd6jL9vee7bAMG8BsWXkt2nMsV+ODKC5oeC15id3ETb9439YATRmbl6A1oY8hYJPXvLvyOyIuKP6XV7SNM3t8V93Q+v9A6NJ1aeFpb4vk8vPdS9id5JAF/g2rJCIQpqmTipPMEQGaY5yoczhUO9gdYqdWsJT2JpZYXtjKAmPM0x2KrP+owPA/zRbeEc4j38pj6vJJ+EFUXEbUlw/2QFChio1WvTItS9W03EU2hxaG9eTEAd4EXYEirKt9c8rCRHGqmgCBRkaLeLLadexvSZaspR8mp1e6JwLnuQ/RZJEKoxSL2H7mVB0vRTFvHAs99ANoMOtxGVOEme0PX2lPZwMkUVBWNsj/HY/QWqP/oxKs0+fJbujcHZ37GZhaAe+kkOPWfclu458ab5sR0TT4Ui18AxXgyJC4Y1Vrf0XQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 01, 2026 at 03:21:18AM -0700, Usama Arif wrote: > The force_thp_readahead path in do_sync_mmap_readahead() is gated on > HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER and always requests > HPAGE_PMD_ORDER / HPAGE_PMD_NR. On configurations where HPAGE_PMD_ORDER > exceeds MAX_PAGECACHE_ORDER, notably arm64 with a 64K base page size, > VM_HUGEPAGE mappings cannot use this path and fall back to the non-forced > mmap readahead path even when the mapping supports useful large folios. > > Enable forced readahead for mappings that support large folios and request > the max folio order supported by the mapping, capped at 2M. > 2MB is chosen as the cap because it matches the PMD size on x86_64 > and on arm64 with 4K base pages, so the size/memory-pressure tradeoff > for folios of that size is already well understood. On arm64 with 16K > and 64K base page sizes, 2MB is also the contiguous-PTE (contpte) > block size, so the resulting folios coalesce into a single TLB entry > and reduce TLB pressure on the readahead path. This will result > in 32M folios not being faulted in with 16K base page size for arm64, > but with contpte, the performance difference should be negligible. > > The final allocation order may still be clamped by page_cache_ra_order() > to the mapping and request geometry, but this gives VM_HUGEPAGE mappings > on such configurations a large-folio readahead request instead of > dropping back to base-page readahead. > > Signed-off-by: Usama Arif Reviewed-by: Pedro Falcato Overall LGTM. Lets see if performance doesn't degrade. /me hides in cover -- Pedro