From 529ce23a764f25d172198b4c6ba90f1e2ad17f93 Mon Sep 17 00:00:00 2001 From: Rick Edgecombe Date: Mon, 25 Mar 2024 19:16:44 -0700 Subject: mm: switch mm->get_unmapped_area() to a flag The mm_struct contains a function pointer *get_unmapped_area(), which is set to either arch_get_unmapped_area() or arch_get_unmapped_area_topdown() during the initialization of the mm. Since the function pointer only ever points to two functions that are named the same across all arch's, a function pointer is not really required. In addition future changes will want to add versions of the functions that take additional arguments. So to save a pointers worth of bytes in mm_struct, and prevent adding additional function pointers to mm_struct in future changes, remove it and keep the information about which get_unmapped_area() to use in a flag. Add the new flag to MMF_INIT_MASK so it doesn't get clobbered on fork by mmf_init_flags(). Most MM flags get clobbered on fork. In the pre-existing behavior mm->get_unmapped_area() would get copied to the new mm in dup_mm(), so not clobbering the flag preserves the existing behavior around inheriting the topdown-ness. Introduce a helper, mm_get_unmapped_area(), to easily convert code that refers to the old function pointer to instead select and call either arch_get_unmapped_area() or arch_get_unmapped_area_topdown() based on the flag. Then drop the mm->get_unmapped_area() function pointer. Leave the get_unmapped_area() pointer in struct file_operations alone. The main purpose of this change is to reorganize in preparation for future changes, but it also converts the calls of mm->get_unmapped_area() from indirect branches into a direct ones. The stress-ng bigheap benchmark calls realloc a lot, which calls through get_unmapped_area() in the kernel. On x86, the change yielded a ~1% improvement there on a retpoline config. In testing a few x86 configs, removing the pointer unfortunately didn't result in any actual size reductions in the compiled layout of mm_struct. But depending on compiler or arch alignment requirements, the change could shrink the size of mm_struct. Link: https://lkml.kernel.org/r/20240326021656.202649-3-rick.p.edgecombe@intel.com Signed-off-by: Rick Edgecombe Acked-by: Dave Hansen Acked-by: Liam R. Howlett Reviewed-by: Kirill A. Shutemov Acked-by: Alexei Starovoitov Cc: Dan Williams Cc: Andy Lutomirski Cc: Aneesh Kumar K.V Cc: Borislav Petkov (AMD) Cc: Christophe Leroy Cc: Deepak Gupta Cc: Guo Ren Cc: Helge Deller Cc: H. Peter Anvin (Intel) Cc: Ingo Molnar Cc: "James E.J. Bottomley" Cc: Kees Cook Cc: Mark Brown Cc: Michael Ellerman Cc: Naveen N. Rao Cc: Nicholas Piggin Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- mm/debug.c | 6 ------ 1 file changed, 6 deletions(-) (limited to 'mm/debug.c') diff --git a/mm/debug.c b/mm/debug.c index e8a96b8b7197..b71186f1fb0b 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -177,9 +177,6 @@ EXPORT_SYMBOL(dump_vma); void dump_mm(const struct mm_struct *mm) { pr_emerg("mm %px task_size %lu\n" -#ifdef CONFIG_MMU - "get_unmapped_area %px\n" -#endif "mmap_base %lu mmap_legacy_base %lu\n" "pgd %px mm_users %d mm_count %d pgtables_bytes %lu map_count %d\n" "hiwater_rss %lx hiwater_vm %lx total_vm %lx locked_vm %lx\n" @@ -205,9 +202,6 @@ void dump_mm(const struct mm_struct *mm) "def_flags: %#lx(%pGv)\n", mm, mm->task_size, -#ifdef CONFIG_MMU - mm->get_unmapped_area, -#endif mm->mmap_base, mm->mmap_legacy_base, mm->pgd, atomic_read(&mm->mm_users), atomic_read(&mm->mm_count), -- cgit v1.2.3-59-g8ed1b