Madhavan Srinivasan wrote: > On Tuesday 20 May 2014 03:57 PM, Kirill A. Shutemov wrote: > > Rusty Russell wrote: > >> "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes: > >>> Andrew Morton wrote: > >>>> On Mon, 19 May 2014 16:23:07 -0700 (PDT) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > >>>> > >>>>> Shouldn't FAULT_AROUND_ORDER and fault_around_order be changed to be > >>>>> the order of the fault-around size in bytes, and fault_around_pages() > >>>>> use 1UL << (fault_around_order - PAGE_SHIFT) > >>>> > >>>> Yes. And shame on me for missing it (this time!) at review. > >>>> > >>>> There's still time to fix this. Patches, please. > >>> > >>> Here it is. Made at 3.30 AM, build tested only. > >> > >> Prefer on top of Maddy's patch which makes it always a variable, rather > >> than CONFIG_DEBUG_FS. It's got enough hair as it is. > > > > Something like this? > > > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > > Date: Tue, 20 May 2014 13:02:03 +0300 > > Subject: [PATCH] mm: nominate faultaround area in bytes rather then page order > > > > There are evidences that faultaround feature is less relevant on > > architectures with page size bigger then 4k. Which makes sense since > > page fault overhead per byte of mapped area should be less there. > > > > Let's rework the feature to specify faultaround area in bytes instead of > > page order. It's 64 kilobytes for now. > > > > The patch effectively disables faultaround on architectures with > > page size >= 64k (like ppc64). > > > > It's possible that some other size of faultaround area is relevant for a > > platform. We can expose `fault_around_bytes' variable to arch-specific > > code once such platforms will be found. > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > --- > > mm/memory.c | 62 +++++++++++++++++++++++-------------------------------------- > > 1 file changed, 23 insertions(+), 39 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 037b812a9531..252b319e8cdf 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -3402,63 +3402,47 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address, > > update_mmu_cache(vma, address, pte); > > } > > > > -#define FAULT_AROUND_ORDER 4 > > +static unsigned long fault_around_bytes = 65536; > > + > > +static inline unsigned long fault_around_pages(void) > > +{ > > + return rounddown_pow_of_two(fault_around_bytes) / PAGE_SIZE; > > +} > > + > > +static inline unsigned long fault_around_mask(void) > > +{ > > + return ~(rounddown_pow_of_two(fault_around_bytes) - 1) & PAGE_MASK; > > +} > > > > -#ifdef CONFIG_DEBUG_FS > > -static unsigned int fault_around_order = FAULT_AROUND_ORDER; > > > > -static int fault_around_order_get(void *data, u64 *val) > > +#ifdef CONFIG_DEBUG_FS > > +static int fault_around_bytes_get(void *data, u64 *val) > > { > > - *val = fault_around_order; > > + *val = fault_around_bytes; > > return 0; > > } > > > > -static int fault_around_order_set(void *data, u64 val) > > +static int fault_around_bytes_set(void *data, u64 val) > > { > > Kindly ignore the question if not relevant. Even though we need root > access to alter the value, will we be fine with > negative value?. val is u64. or I miss something? -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>