Adding fast code paths to handle specifically only get and/or clear operation of PAGE_IS_WRITTEN, increases its performance by 0-35%. The results of some test cases are given below:
Test-case-1 t1 = (Get + WP) time t2 = WP time t1 t2 Without this patch: 140-170mcs 90-115mcs With this patch: 110mcs 80mcs Worst case diff: 35% faster 30% faster
Test-case-2 t3 = atomic Get and WP t3 Without this patch: 120-140mcs With this patch: 100-110mcs Worst case diff: 21% faster
Signed-off-by: Muhammad Usama Anjum usama.anjum@collabora.com --- The test to measure the performance can be found: https://is.gd/FtSKcD 8 8192 3 1 0 and 8 8192 3 1 1 arguments have been used to produce the above mentioned results.
Changes in v29: - Minor updates in flush logic following the original patch --- fs/proc/task_mmu.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 0903e10e5fc08..5b61ba093ff3e 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -2121,6 +2121,41 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, return 0; }
+ if (!p->vec_out) { + /* Fast path for performing exclusive WP */ + for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { + if (pte_uffd_wp(ptep_get(pte))) + continue; + make_uffd_wp_pte(vma, addr, pte); + if (!flush_end) + start = addr; + flush_end = addr + PAGE_SIZE; + } + goto flush_and_return; + } + + if (!p->arg.category_anyof_mask && !p->arg.category_inverted && + p->arg.category_mask == PAGE_IS_WRITTEN && + p->arg.return_mask == PAGE_IS_WRITTEN) { + for (addr = start; addr < end; pte++, addr += PAGE_SIZE) { + unsigned long next = addr + PAGE_SIZE; + + if (pte_uffd_wp(ptep_get(pte))) + continue; + ret = pagemap_scan_output(p->cur_vma_category | PAGE_IS_WRITTEN, + p, addr, &next); + if (next == addr) + break; + if (~p->arg.flags & PM_SCAN_WP_MATCHING) + continue; + make_uffd_wp_pte(vma, addr, pte); + if (!flush_end) + start = addr; + flush_end = next; + } + goto flush_and_return; + } + for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { unsigned long categories = p->cur_vma_category | pagemap_page_category(p, vma, addr, ptep_get(pte)); @@ -2144,6 +2179,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, flush_end = next; }
+flush_and_return: if (flush_end) flush_tlb_range(vma, start, addr);