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b=M8Zx0AuJEuSPkF07I/Ib4o3GDx/OLKcdDOkXqcU3T5+YDru7awKHBAqruc4v19NBh StSU8ZRucJPgwNH8201LF0ej6+1EMiJCIXBoEXMJf8a6TfGzE/bP8WQp1JHd8ZUAla qwYYfHpAfH/3vdfi0eIJt+O942Vv75P+thTYrqRSZ6L91LYZz6mHODG1A2ccSWgEYY bqL1Iui6q718lMcZmN7DmkKE7LQ1DYM4IiCXQm24u4Fy+HNwLFoseaAULcYVaiq8dq AViedRoS1YAVrRPNKDoQWeYzJ7ckZJNJwTjnWAX1cpdGwr/cgWENs/A/ENjyYgFEWo SD20UDN3q8nZw== Message-ID: Date: Thu, 19 Mar 2026 08:35:30 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] arm64: request contpte-sized folios for exec memory 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 References: <20260310145406.3073394-1-usama.arif@linux.dev> <20260310145406.3073394-2-usama.arif@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-Rspam-User: X-Rspamd-Queue-Id: B14FAA0002 X-Rspamd-Server: rspam08 X-Stat-Signature: ciwt84apiz96bfxertr9ugrro4fww9c6 X-HE-Tag: 1773905739-605011 X-HE-Meta: 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 Z1TxMksP PlTNsw6mplKAXk4L63hthkzgEb7Ur+yw041C/db6pAzH2EKBKoYeS4wbuKixMRrCD6vJU/HsLFuDtP0Op0ksAy21hJ8I7XFqFJGj6LSpisxkhrHk61Qj5cG6BdVKav2smAXOBhV6+0eivD7zC+4xsCkjcQQ03nqqpvTr53gjCxyiCjIS23nlptB05xPAxKjYwt2jyaBQc2IU1Rwvuu9sOk6rwx3D9yGqNm9DgOREcoFQT9alP0DsK5yqLwAk89Ck5G7A6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/10/26 15:51, Usama Arif wrote: > exec_folio_order() was introduced [1] to request readahead of executable > file-backed pages at an arch-preferred folio order, so that the hardware > can coalesce contiguous PTEs into fewer iTLB entries (contpte). > > The current implementation uses ilog2(SZ_64K >> PAGE_SHIFT), which > requests 64K folios. This is optimal for 4K base pages (where CONT_PTES > = 16, contpte size = 64K), but suboptimal for 16K and 64K base pages: > > Page size | Before (order) | After (order) | contpte > ----------|----------------|---------------|-------- > 4K | 4 (64K) | 4 (64K) | Yes (unchanged) > 16K | 2 (64K) | 7 (2M) | Yes (new) > 64K | 0 (64K) | 5 (2M) | Yes (new) > > For 16K pages, CONT_PTES = 128 and the contpte size is 2M (order 7). > For 64K pages, CONT_PTES = 32 and the contpte size is 2M (order 5). > > Use ilog2(CONT_PTES) instead, which directly evaluates to contpte-aligned > order for all page sizes. > > The worst-case waste is bounded to one folio (up to 2MB - 64KB) > at the end of the file, since page_cache_ra_order() reduces the folio > order near EOF to avoid allocating past i_size. So, if you have a smallish text segment in a larger file, we'd always try to allocate 2M on 16k/64k? That feels wrong. Asking the other way around: why not also use 2M on a 4k system and end up with a PMD? And no, I don't think we should default to that, just emphasizing my point that *maybe* we really want to consider mapping (vma) size as well. -- Cheers, David