On 17/04/2023 09:25, Yin, Fengwei wrote: > > > On 4/14/2023 9:03 PM, Ryan Roberts wrote: >> When allocating large anonymous folios, we want to maximize our chances >> of being able to use the highest order we support. Since one of the >> constraints is that a folio has to be mapped naturally aligned, let's >> have mmap default to that alignment when user space does not provide a >> hint. >> >> With this in place, an extra 2% of all allocated anonymous memory >> belongs to a folio of the highest order, when compiling the kernel. > This change has side effect: reduce the chance of VMA merging. > So benefit to per-VMA lock also. But find VMA need searching more VMAs. Good point. This change brings only a very marginal benefit anyway, so I think I might just drop the it from the series to avoid any unexpected issues. > > > Regards > Yin, Fengwei > >> >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> --- >> mm/mmap.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/mm/mmap.c b/mm/mmap.c >> index ff68a67a2a7c..e7652001a32e 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -1627,7 +1627,7 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr, >> info.length = len; >> info.low_limit = mm->mmap_base; >> info.high_limit = mmap_end; >> - info.align_mask = 0; >> + info.align_mask = BIT(PAGE_SHIFT + ANON_FOLIO_ORDER_MAX) - 1; >> info.align_offset = 0; >> return vm_unmapped_area(&info); >> } >> @@ -1677,7 +1677,7 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr, >> info.length = len; >> info.low_limit = max(PAGE_SIZE, mmap_min_addr); >> info.high_limit = arch_get_mmap_base(addr, mm->mmap_base); >> - info.align_mask = 0; >> + info.align_mask = BIT(PAGE_SHIFT + ANON_FOLIO_ORDER_MAX) - 1; >> info.align_offset = 0; >> addr = vm_unmapped_area(&info); >> >> -- >> 2.25.1 >>
