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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1w3cF7-000000080Fh-2VkZ; Fri, 20 Mar 2026 15:58:33 +0000 Date: Fri, 20 Mar 2026 15:58:33 +0000 From: Matthew Wilcox To: Usama Arif Cc: Andrew Morton , david@kernel.org, ryan.roberts@arm.com, linux-mm@kvack.org, r@hev.cc, jack@suse.cz, ajd@linux.ibm.com, 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.Howlett@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, lorenzo.stoakes@oracle.com, 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 , wilts.infradead.org@kvack.org, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com Subject: Re: [PATCH v2 3/4] elf: align ET_DYN base to max folio size for PTE coalescing Message-ID: References: <20260320140315.979307-1-usama.arif@linux.dev> <20260320140315.979307-4-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260320140315.979307-4-usama.arif@linux.dev> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 42EAE20002 X-Stat-Signature: 157ob55k17e6zcs8sppekjf6ofztyuhc X-Rspam-User: X-HE-Tag: 1774022322-364125 X-HE-Meta: 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 i0yELVbS yVH3RxWTwEObesKvDM94juCLWUAg+FIncA0k4ilBbRcM4Q624p6WL/jtoAK69Fd1QqT7uTXLNXXl6lk5MQWy7pmWm3I9dCQonOFte4SPjnOothXCs8OBlUO4OqvRoN8Z8MfjwjdF0C/ExoIa2sCMUmhD/jM0CIWRA027wxypx5KwZc0ZhYxQem0vj02yght//ksvoB9lXu0DTSsYQTl72mLF9Twu4MjYi7G5W6Ms4oH9kE3UG7mb2n0yux8hhYxvG90omwH1S054INjqrmof6M8Z7dP10VrmcSQecaajyOESuUSMPSS8UvB/hi7Mp2k36kgQn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 20, 2026 at 06:58:53AM -0700, Usama Arif wrote: > -static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr) > +static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr, > + struct file *filp) > { > unsigned long alignment = 0; > + unsigned long max_folio_size = PAGE_SIZE; > int i; > > + if (filp && filp->f_mapping) > + max_folio_size = mapping_max_folio_size(filp->f_mapping); Under what circumstances can bprm->file be NULL? Also we tend to prefer the name "file" rather than "filp" for new code (yes, there's a lot of old code out there). > + > + /* > + * Try to align the binary to the largest folio > + * size that the page cache supports, so the > + * hardware can coalesce PTEs (e.g. arm64 > + * contpte) or use PMD mappings for large folios. > + * > + * Use the largest power-of-2 that fits within > + * the segment size, capped by what the page > + * cache will allocate. Only align when the > + * segment's virtual address and file offset are > + * already aligned to the folio size, as > + * misalignment would prevent coalescing anyway. > + * > + * The segment size check avoids reducing ASLR > + * entropy for small binaries that cannot > + * benefit. > + */ > + if (!cmds[i].p_filesz) > + continue; > + size = rounddown_pow_of_two(cmds[i].p_filesz); > + size = min(size, max_folio_size); > + if (size > PAGE_SIZE && > + IS_ALIGNED(cmds[i].p_vaddr, size) && > + IS_ALIGNED(cmds[i].p_offset, size)) > + alignment = max(alignment, size); Can this not all be factored out into a different function? Also, I think it was done a bit better here: https://lore.kernel.org/linux-fsdevel/20260313005211.882831-1-r@hev.cc/ + if (!IS_ALIGNED(cmd->p_vaddr | cmd->p_offset, PMD_SIZE)) + return false;