[PATCH 4/5] mm: add force_free_pages in zap_pte_range

Aaron Lu
2017-02-24T11:41:04Z

force_flush in zap_pte_range is set in the following 2 conditions:
1 When no more batches can be allocated (either due to no memory or
MAX_GATHER_BATCH_COUNT has reached) to store those to-be-freed page
pointers;
2 When a TLB_only flush is needed before dropping the PTE lock to avoid
a race condition as explained in commit 1cf35d47712d
("mm: split 'tlb_flush_mmu()' into tlb flushing and memory freeing parts").

Once force_flush is set, the pages accumulated thus far will all be
freed. Since there is no need to do page free if condition 2 occurred,
add a new variable named force_free_pages to decide if page free should
be done and it will only only be set if condition 1 occured.

With this change, the page accumulation will not be interrupted by
condition 2 anymore. In the meantime, rename force_flush to
force_flush_tlb for condition 2.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
mm/memory.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index eb8b17fc1b2b..7d1fe74084be 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1185,7 +1185,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
struct zap_details *details)
{
struct mm_struct *mm = tlb->mm;
- int force_flush = 0;
+ int force_flush_tlb = 0, force_free_pages = 0;
int rss[NR_MM_COUNTERS];
spinlock_t *ptl;
pte_t *start_pte;
@@ -1232,7 +1232,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
*/
if (unlikely(details && details->ignore_dirty))
continue;
- force_flush = 1;
+ force_flush_tlb = 1;
set_page_dirty(page);
}
if (pte_young(ptent) &&
@@ -1244,7 +1244,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
if (unlikely(page_mapcount(page) < 0))
print_bad_pte(vma, addr, ptent, page);
if (unlikely(__tlb_remove_page(tlb, page))) {
- force_flush = 1;
+ force_free_pages = 1;
addr += PAGE_SIZE;
break;
}
@@ -1272,18 +1272,14 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
arch_leave_lazy_mmu_mode();

/* Do the actual TLB flush before dropping ptl */
- if (force_flush)
+ if (force_flush_tlb) {
+ force_flush_tlb = 0;
tlb_flush_mmu_tlbonly(tlb);
+ }
pte_unmap_unlock(start_pte, ptl);

- /*
- * If we forced a TLB flush (either due to running out of
- * batch buffers or because we needed to flush dirty TLB
- * entries before releasing the ptl), free the batched
- * memory too. Restart if we didn't do everything.
- */
- if (force_flush) {
- force_flush = 0;
+ if (force_free_pages) {
+ force_free_pages = 0;
tlb_flush_mmu_free(tlb);
if (addr != end)
goto again;
--
2.9.3