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b=OYbuI4Mi7c5qsUy/G/ZYGrvOHFCTW/szfFBZDvDH5aP8kIIRGZbUSLe3/qhHSrc/Y 41rmRqo4gXjwtcd2pIfDtDknzJR/xDeA+GOJXyeDS1IBuazpueGcf+FqLyyKCVAiGH FA6ikYq18iYHNxP26mEdGY87syEk0AhR9k3CgUR/3F7Njsz+gc+bdyfihYE2u5XssX vgV7L7EjIhROfN0YidaQoPfiknxjUtXy9WkAZUlfT9zyCwW254gDon8u0nSJV4vCLz b2Um5Mc5dec1zf/Povf0u+Gh4REpE7RGbho1tXzu40Rz4eU5kxTb8mNQnrx8/CruWb 24sGJW49WJBXQ== Message-ID: Date: Wed, 18 Mar 2026 13:41:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/4] arm64/mm: contpte-sized exec folios for 16K and 64K pages To: Usama Arif , Andrew Morton , ryan.roberts@arm.com Cc: ajd@linux.ibm.com, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, brauner@kernel.org, catalin.marinas@arm.com, dev.jain@arm.com, jack@suse.cz, kees@kernel.org, kevin.brodsky@arm.com, lance.yang@linux.dev, Liam.Howlett@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, rmclure@linux.ibm.com, Al Viro , will@kernel.org, willy@infradead.org, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com, WANG Rui References: <20260310145406.3073394-1-usama.arif@linux.dev> <608c87ce-10d9-4012-b6e9-298d5a356801@kernel.org> <9e9edebb-3953-4bcd-80e2-614dcec5b402@linux.dev> <562fb349-c2d2-4fbe-83f9-75c26cc4b7ae@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 849E0120012 X-Stat-Signature: 18eh7bxqfupixuw3yyndjax7q5xzzh51 X-Rspam-User: X-HE-Tag: 1773837681-113723 X-HE-Meta: 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 3QhoDWN4 JJYt34lPNOCdtuXwpwa4PdZaKFVFAlwFzr/pFE5oR8BlyXrWQ4nFW72PBqaKeR70n8yUYouWN+RlejzjuByg05bUVZDERdmcxR1p6B70CufyYXBDHmazA1aHtMfux1bVOb31AsppsPSRCSHDwrbeQm6k9O3fF8QVowgGtadmqsohB1+NcN00byXqN711HQHQaih0GP8C6qQqiK6bR55YBhzMOlCVPEr56SsjNOuU+Y6qPF1z5Gt2uONV/RqU9HjPf7SJP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/18/26 11:41, Usama Arif wrote: > > > On 16/03/2026 19:06, David Hildenbrand (Arm) wrote: >> On 3/13/26 20:59, Usama Arif wrote: >>> >>> >>> >>> So I see 2 benefits from this. Page fault and iTLB coverage. IMHO page >>> faults are not that big of a deal? If the text section is hot, it wont >>> get flushed after faulting in. So the real benefit comes from improved >>> iTLB coverage. >>> >>> For a 128M mapping, 2M alignment gives 64 contpte entries. Aligning >>> to something larger (say 128M) wouldn't give any additional TLB >>> coalescing, each 2M-aligned region independently qualifies for contpte. >>> >>> Mappings smaller than 2M can't benefit from contpte regardless of >>> alignment, so falling back to PAGE_SIZE would be the optimal behaviour. >>> Adding intermediate sizes (e.g. 512K, 128K) wouldn't map to any >>> hardware boundary and adds complexity without TLB benefit? >> >> I might be wrong, but I think you are mixing two things here: >> >> (1) "Minimum" folio size (exec_folio_order()) >> >> (2) VMA alignment. >> >> >> (2) should certainly be as large as (1), but assume we can get a 2M >> folio on arm64 4k, why shouldn't we align it to 2M if the region is >> reasonably sized, and use a PMD? >> >> > > So this series is tackling both (1) and (2). When I started making changes > to the code, what I wanted was 2M folios at fault with 64K base page size > to reduce iTLB misses. This is what patch 1 (and 2) will achieve. > > Yes, completely agree, (2) should be as large as (1). I didn't think about > PMD size on 4K which you pointed out. do_sync_mmap_readahead can give > that with force_thp_readahead, so this should be supported. In particular, imagine if hw starts optimizing transparently on other granularity, then the "smallest granularity" (exec_folio_order()) decision will soon be wrong. > > But we shouldn't align to PMD size for all base page sizes. As Rui pointed > out, increasing alignment size reduces ASLR entropy [1]. Should we max alignement > to 2M? That's why I said that likely, as an input, we'd want to use the mapping size or other heuristics. We wouldn't want to align a 4k mapping to either 64k or 2M. Long story short: the change in thp_get_unmapped_area_vmflags() needs some thought IMHO. -- Cheers, David