| Message ID | 20230414130303.2345383-17-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | variable-order, large folios for anonymous memory | expand |
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. Regards Yin, Fengwei > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- > 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 >
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@arm.com> >> --- >> 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 >>
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);
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. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- mm/mmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.25.1