On Thu, Feb 15, 2024 at 03:13:25PM -0800, Rick Edgecombe wrote: > 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. > > 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 ~4% > improvement there. (bogo ops/s (usr+sys time)) > > 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 > possibly shrink the size of mm_struct. > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> > --- > arch/s390/mm/hugetlbpage.c | 2 +- > arch/s390/mm/mmap.c | 4 ++-- > arch/sparc/kernel/sys_sparc_64.c | 15 ++++++--------- > arch/sparc/mm/hugetlbpage.c | 2 +- > arch/x86/kernel/cpu/sgx/driver.c | 2 +- > arch/x86/mm/hugetlbpage.c | 2 +- > arch/x86/mm/mmap.c | 4 ++-- > drivers/char/mem.c | 2 +- > drivers/dax/device.c | 6 +++--- > fs/hugetlbfs/inode.c | 2 +- > fs/proc/inode.c | 15 ++++++++------- > fs/ramfs/file-mmu.c | 2 +- > include/linux/mm_types.h | 6 +----- > include/linux/sched/coredump.h | 1 + > include/linux/sched/mm.h | 5 +++++ > io_uring/io_uring.c | 2 +- > mm/debug.c | 6 ------ > mm/huge_memory.c | 6 +++--- > mm/mmap.c | 21 ++++++++++++++++++--- > mm/shmem.c | 11 +++++------ > mm/util.c | 6 +++--- > 21 files changed, 65 insertions(+), 57 deletions(-) > > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index 02f5090ffea2..428e440424c5 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -74,6 +74,7 @@ static inline int get_dumpable(struct mm_struct *mm) > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) > #define MMF_OOM_REAP_QUEUED 25 /* mm was queued for oom_reaper */ > #define MMF_MULTIPROCESS 26 /* mm is shared between processes */ > +#define MMF_TOPDOWN 27 /* mm is shared between processes */ Nit: you may want to update the comment here ;-) > /* > * MMF_HAS_PINNED: Whether this mm has pinned any pages. This can be either > * replaced in the future by mm.pinned_vm when it becomes stable, or grow into -- Sincerely yours, Mike.
