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Date: Wed, 09 Jan 2013 13:15:39 +1100
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Michel Lespinasse <walken@...gle.com>
Cc: Rik van Riel <riel@...hat.com>,
"James E.J. Bottomley" <jejb@...isc-linux.org>,
Matt Turner <mattst88@...il.com>,
David Howells <dhowells@...hat.com>,
Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
linuxppc-dev@...ts.ozlabs.org, linux-parisc@...r.kernel.org,
linux-alpha@...r.kernel.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH 7/8] mm: use vm_unmapped_area() on powerpc architecture
On Tue, 2013-01-08 at 17:28 -0800, Michel Lespinasse wrote:
> Update the powerpc slice_get_unmapped_area function to make use of
> vm_unmapped_area() instead of implementing a brute force search.
>
> Signed-off-by: Michel Lespinasse <walken@...gle.com>
>
> ---
> arch/powerpc/mm/slice.c | 128 +++++++++++++++++++++++++++++-----------------
> 1 files changed, 81 insertions(+), 47 deletions(-)
That doesn't look good ... the resulting code is longer than the
original, which makes me wonder how it is an improvement...
Now it could just be a matter of how the code is factored, I see
quite a bit of duplication of the whole slice mask test...
Cheers,
Ben.
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 999a74f25ebe..048346b7eed5 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -242,31 +242,51 @@ static unsigned long slice_find_area_bottomup(struct mm_struct *mm,
> struct slice_mask available,
> int psize)
> {
> - struct vm_area_struct *vma;
> - unsigned long addr;
> - struct slice_mask mask;
> int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
> + unsigned long addr, found, slice;
> + struct vm_unmapped_area_info info;
>
> - addr = TASK_UNMAPPED_BASE;
> + info.flags = 0;
> + info.length = len;
> + info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
> + info.align_offset = 0;
>
> - for (;;) {
> - addr = _ALIGN_UP(addr, 1ul << pshift);
> - if ((TASK_SIZE - len) < addr)
> - break;
> - vma = find_vma(mm, addr);
> - BUG_ON(vma && (addr >= vma->vm_end));
> + addr = TASK_UNMAPPED_BASE;
> + while (addr < TASK_SIZE) {
> + info.low_limit = addr;
> + if (addr < SLICE_LOW_TOP) {
> + slice = GET_LOW_SLICE_INDEX(addr);
> + addr = (slice + 1) << SLICE_LOW_SHIFT;
> + if (!(available.low_slices & (1u << slice)))
> + continue;
> + } else {
> + slice = GET_HIGH_SLICE_INDEX(addr);
> + addr = (slice + 1) << SLICE_HIGH_SHIFT;
> + if (!(available.high_slices & (1u << slice)))
> + continue;
> + }
>
> - mask = slice_range_to_mask(addr, len);
> - if (!slice_check_fit(mask, available)) {
> - if (addr < SLICE_LOW_TOP)
> - addr = _ALIGN_UP(addr + 1, 1ul << SLICE_LOW_SHIFT);
> - else
> - addr = _ALIGN_UP(addr + 1, 1ul << SLICE_HIGH_SHIFT);
> - continue;
> + next_slice:
> + if (addr >= TASK_SIZE)
> + addr = TASK_SIZE;
> + else if (addr < SLICE_LOW_TOP) {
> + slice = GET_LOW_SLICE_INDEX(addr);
> + if (available.low_slices & (1u << slice)) {
> + addr = (slice + 1) << SLICE_LOW_SHIFT;
> + goto next_slice;
> + }
> + } else {
> + slice = GET_HIGH_SLICE_INDEX(addr);
> + if (available.high_slices & (1u << slice)) {
> + addr = (slice + 1) << SLICE_HIGH_SHIFT;
> + goto next_slice;
> + }
> }
> - if (!vma || addr + len <= vma->vm_start)
> - return addr;
> - addr = vma->vm_end;
> + info.high_limit = addr;
> +
> + found = vm_unmapped_area(&info);
> + if (!(found & ~PAGE_MASK))
> + return found;
> }
>
> return -ENOMEM;
> @@ -277,39 +297,53 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
> struct slice_mask available,
> int psize)
> {
> - struct vm_area_struct *vma;
> - unsigned long addr;
> - struct slice_mask mask;
> int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
> + unsigned long addr, found, slice;
> + struct vm_unmapped_area_info info;
>
> - addr = mm->mmap_base;
> - while (addr > len) {
> - /* Go down by chunk size */
> - addr = _ALIGN_DOWN(addr - len, 1ul << pshift);
> + info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> + info.length = len;
> + info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
> + info.align_offset = 0;
>
> - /* Check for hit with different page size */
> - mask = slice_range_to_mask(addr, len);
> - if (!slice_check_fit(mask, available)) {
> - if (addr < SLICE_LOW_TOP)
> - addr = _ALIGN_DOWN(addr, 1ul << SLICE_LOW_SHIFT);
> - else if (addr < (1ul << SLICE_HIGH_SHIFT))
> - addr = SLICE_LOW_TOP;
> - else
> - addr = _ALIGN_DOWN(addr, 1ul << SLICE_HIGH_SHIFT);
> - continue;
> + addr = mm->mmap_base;
> + while (addr > PAGE_SIZE) {
> + info.high_limit = addr;
> + if (addr < SLICE_LOW_TOP) {
> + slice = GET_LOW_SLICE_INDEX(addr - 1);
> + addr = slice << SLICE_LOW_SHIFT;
> + if (!(available.low_slices & (1u << slice)))
> + continue;
> + } else {
> + slice = GET_HIGH_SLICE_INDEX(addr - 1);
> + addr = slice ? (slice << SLICE_HIGH_SHIFT) :
> + SLICE_LOW_TOP;
> + if (!(available.high_slices & (1u << slice)))
> + continue;
> }
>
> - /*
> - * Lookup failure means no vma is above this address,
> - * else if new region fits below vma->vm_start,
> - * return with success:
> - */
> - vma = find_vma(mm, addr);
> - if (!vma || (addr + len) <= vma->vm_start)
> - return addr;
> + next_slice:
> + if (addr < PAGE_SIZE)
> + addr = PAGE_SIZE;
> + else if (addr < SLICE_LOW_TOP) {
> + slice = GET_LOW_SLICE_INDEX(addr - 1);
> + if (available.low_slices & (1u << slice)) {
> + addr = slice << SLICE_LOW_SHIFT;
> + goto next_slice;
> + }
> + } else {
> + slice = GET_HIGH_SLICE_INDEX(addr - 1);
> + if (available.high_slices & (1u << slice)) {
> + addr = slice ? (slice << SLICE_HIGH_SHIFT) :
> + SLICE_LOW_TOP;
> + goto next_slice;
> + }
> + }
> + info.low_limit = addr;
>
> - /* try just below the current vma->vm_start */
> - addr = vma->vm_start;
> + found = vm_unmapped_area(&info);
> + if (!(found & ~PAGE_MASK))
> + return found;
> }
>
> /*
--
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