The patch titled
Subject: mm: release the spinlock on zap_pte_range
has been added to the -mm tree. Its filename is
mm-release-the-spinlock-on-zap_pte_range.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-release-the-spinlock-on-zap_pte_range.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-release-the-spinlock-on-zap_pte_range.patch
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------------------------------------------------------
From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: mm: release the spinlock on zap_pte_range
In our testing (camera recording), Miguel and Wei found unmap_page_range()
takes above 6ms with preemption disabled easily. When I see that, the
reason is it holds page table spinlock during entire 512 page operation in
a PMD. 6.2ms is never trivial for user experince if RT task couldn't run
in the time because it could make frame drop or glitch audio problem.
I had a time to benchmark it via adding some trace_printk hooks between
pte_offset_map_lock and pte_unmap_unlock in zap_pte_range. The testing
device is 2018 premium mobile device.
I can get 2ms delay rather easily to release 2M(ie, 512 pages) when the
task runs on little core even though it doesn't have any IPI and LRU lock
contention. It's already too heavy.
If I remove activate_page, 35-40% overhead of zap_pte_range is gone so
most of overhead(about 0.7ms) comes from activate_page via
mark_page_accessed. Thus, if there are LRU contention, that 0.7ms could
accumulate up to several ms.
So this patch adds preemption point for once every 32 times in the loop.
Link: http://lkml.kernel.org/r/20190731061440.GC155569@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Reported-by: Miguel de Dios <migueldedios@xxxxxxxxxx>
Reported-by: Wei Wang <wvw@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
--- a/mm/memory.c~mm-release-the-spinlock-on-zap_pte_range
+++ a/mm/memory.c
@@ -1007,6 +1007,7 @@ static unsigned long zap_pte_range(struc
struct zap_details *details)
{
struct mm_struct *mm = tlb->mm;
+ int progress = 0;
int force_flush = 0;
int rss[NR_MM_COUNTERS];
spinlock_t *ptl;
@@ -1022,7 +1023,15 @@ again:
flush_tlb_batched_pending(mm);
arch_enter_lazy_mmu_mode();
do {
- pte_t ptent = *pte;
+ pte_t ptent;
+
+ if (progress++ >= 32) {
+ progress = 0;
+ if (need_resched())
+ break;
+ }
+
+ ptent = *pte;
if (pte_none(ptent))
continue;
@@ -1123,8 +1132,11 @@ again:
if (force_flush) {
force_flush = 0;
tlb_flush_mmu(tlb);
- if (addr != end)
- goto again;
+ }
+
+ if (addr != end) {
+ progress = 0;
+ goto again;
}
return addr;
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
mm-release-the-spinlock-on-zap_pte_range.patch
mm-introduce-madv_cold.patch
mm-change-pageref_reclaim_clean-with-page_refreclaim.patch
mm-account-nr_isolated_xxx-in-_lru_page.patch
mm-introduce-madv_pageout.patch
mm-factor-out-common-parts-between-madv_cold-and-madv_pageout.patch
