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?. Regards Maddy > - BUILD_BUG_ON((1UL << FAULT_AROUND_ORDER) > PTRS_PER_PTE); > - if (1UL << val > PTRS_PER_PTE) > + if (val / PAGE_SIZE > PTRS_PER_PTE) > return -EINVAL; > - fault_around_order = val; > + fault_around_bytes = val; > return 0; > } > -DEFINE_SIMPLE_ATTRIBUTE(fault_around_order_fops, > - fault_around_order_get, fault_around_order_set, "%llu\n"); > +DEFINE_SIMPLE_ATTRIBUTE(fault_around_bytes_fops, > + fault_around_bytes_get, fault_around_bytes_set, "%llu\n"); > > static int __init fault_around_debugfs(void) > { > void *ret; > > - ret = debugfs_create_file("fault_around_order", 0644, NULL, NULL, > - &fault_around_order_fops); > + ret = debugfs_create_file("fault_around_bytes", 0644, NULL, NULL, > + &fault_around_bytes_fops); > if (!ret) > - pr_warn("Failed to create fault_around_order in debugfs"); > + pr_warn("Failed to create fault_around_bytes in debugfs"); > return 0; > } > late_initcall(fault_around_debugfs); > - > -static inline unsigned long fault_around_pages(void) > -{ > - return 1UL << fault_around_order; > -} > - > -static inline unsigned long fault_around_mask(void) > -{ > - return ~((1UL << (PAGE_SHIFT + fault_around_order)) - 1); > -} > -#else > -static inline unsigned long fault_around_pages(void) > -{ > - unsigned long nr_pages; > - > - nr_pages = 1UL << FAULT_AROUND_ORDER; > - BUILD_BUG_ON(nr_pages > PTRS_PER_PTE); > - return nr_pages; > -} > - > -static inline unsigned long fault_around_mask(void) > -{ > - return ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1); > -} > #endif > > static void do_fault_around(struct vm_area_struct *vma, unsigned long address, > @@ -3515,7 +3499,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, > * if page by the offset is not ready to be mapped (cold cache or > * something). > */ > - if (vma->vm_ops->map_pages) { > + if (vma->vm_ops->map_pages && fault_around_pages() > 1) { > pte = pte_offset_map_lock(mm, pmd, address, &ptl); > do_fault_around(vma, address, pte, pgoff, flags); > if (!pte_same(*pte, orig_pte)) > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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