p71924506
/
linux_old1
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

x86/mm: Eliminate redundant page table walk during TLB range flushing 

When choosing between doing an address space or ranged flush,
the x86 implementation of flush_tlb_mm_range takes into account
whether there are any large pages in the range.  A per-page
flush typically requires fewer entries than would covered by a
single large page and the check is redundant.

There is one potential exception.  THP migration flushes single
THP entries and it conceivably would benefit from flushing a
single entry instead of the mm.  However, this flush is after a
THP allocation, copy and page table update potentially with any
other threads serialised behind it.  In comparison to that, the
flush is noise.  It makes more sense to optimise balancing to
require fewer flushes than to optimise the flush itself.

This patch deletes the redundant huge page check.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Tested-by: Davidlohr Bueso <davidlohr@hp.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-sgei1drpOcburujPsfh6ovmo@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mel Gorman 2014-01-21 14:33:19 -08:00 committed by Ingo Molnar
parent 15aa368255
commit 71b54f8263
1 changed files with 1 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
arch/x86/mm/tlb.c
View File

@ -158,32 +158,6 @@ void flush_tlb_current_task(void)
preempt_enable(); preempt_enable();
} }
/*
* It can find out the THP large page, or
* HUGETLB page in tlb_flush when THP disabled
*/
static inline unsigned long has_large_page(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
unsigned long addr = ALIGN(start, HPAGE_SIZE);
for (; addr < end; addr += HPAGE_SIZE) {
pgd = pgd_offset(mm, addr);
if (likely(!pgd_none(*pgd))) {
pud = pud_offset(pgd, addr);
if (likely(!pud_none(*pud))) {
pmd = pmd_offset(pud, addr);
if (likely(!pmd_none(*pmd)))
if (pmd_large(*pmd))
return addr;
}
}
}
return 0;
}
void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
unsigned long end, unsigned long vmflag) unsigned long end, unsigned long vmflag)
{ {
@ -218,7 +192,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
nr_base_pages = (end - start) >> PAGE_SHIFT; nr_base_pages = (end - start) >> PAGE_SHIFT;
/* tlb_flushall_shift is on balance point, details in commit log */ /* tlb_flushall_shift is on balance point, details in commit log */
if (nr_base_pages > act_entries || has_large_page(mm, start, end)) { if (nr_base_pages > act_entries) {
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL); count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
local_flush_tlb(); local_flush_tlb();
} else { } else {