mm/khugepaged: consistently order cc->is_khugepaged and pte_* checks

cc->is_khugepaged is used to predicate the khugepaged-only behavior of
enforcing khugepaged heuristics limited by the sysfs knobs
khugepaged_max_ptes_[none|swap|shared].

In branches where khugepaged_max_ptes_* is checked, consistently check
cc->is_khugepaged first.  Also, local counters (for comparison vs
khugepaged_max_ptes_* limits) were previously incremented in the
comparison expression.  Some of these counters (unmapped) are additionally
used outside of khugepaged_max_ptes_* enforcement, and all counters are
communicated in tracepoints.  Move the correct accounting of these
counters before branching statements to avoid future errors due to C's
short-circuiting evaluation.

Link: https://lkml.kernel.org/r/20220720140603.1958773-3-zokeefe@google.com
Link: https://lore.kernel.org/linux-mm/Ys2qJm6FaOQcxkha@google.com/
Fixes: 9fab4752a181 ("mm/khugepaged: add flag to predicate khugepaged-only behavior")
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: "Souptick Joarder (HPE)" <jrdr.linux@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index c2188745982c072e36422fc62341816440f328c3..ae30794b1ddb2c30d397f1297b3ea2429851c299 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -574,9 +574,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
                pte_t pteval = *_pte;
                if (pte_none(pteval) || (pte_present(pteval) &&
                                is_zero_pfn(pte_pfn(pteval)))) {
+                       ++none_or_zero;
                        if (!userfaultfd_armed(vma) &&
-                           (++none_or_zero <= khugepaged_max_ptes_none ||
-                            !cc->is_khugepaged)) {
+                           (!cc->is_khugepaged ||
+                            none_or_zero <= khugepaged_max_ptes_none)) {
                                continue;
                        } else {
                                result = SCAN_EXCEED_NONE_PTE;
@@ -596,11 +597,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 
                VM_BUG_ON_PAGE(!PageAnon(page), page);
 
-               if (cc->is_khugepaged && page_mapcount(page) > 1 &&
-                   ++shared > khugepaged_max_ptes_shared) {
-                       result = SCAN_EXCEED_SHARED_PTE;
-                       count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-                       goto out;
+               if (page_mapcount(page) > 1) {
+                       ++shared;
+                       if (cc->is_khugepaged &&
+                           shared > khugepaged_max_ptes_shared) {
+                               result = SCAN_EXCEED_SHARED_PTE;
+                               count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
+                               goto out;
+                       }
                }
 
                if (PageCompound(page)) {
@@ -1132,8 +1136,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
             _pte++, _address += PAGE_SIZE) {
                pte_t pteval = *_pte;
                if (is_swap_pte(pteval)) {
-                       if (++unmapped <= khugepaged_max_ptes_swap ||
-                           !cc->is_khugepaged) {
+                       ++unmapped;
+                       if (!cc->is_khugepaged ||
+                           unmapped <= khugepaged_max_ptes_swap) {
                                /*
                                 * Always be strict with uffd-wp
                                 * enabled swap entries.  Please see
@@ -1151,9 +1156,10 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
                        }
                }
                if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+                       ++none_or_zero;
                        if (!userfaultfd_armed(vma) &&
-                           (++none_or_zero <= khugepaged_max_ptes_none ||
-                            !cc->is_khugepaged)) {
+                           (!cc->is_khugepaged ||
+                            none_or_zero <= khugepaged_max_ptes_none)) {
                                continue;
                        } else {
                                result = SCAN_EXCEED_NONE_PTE;
@@ -1183,12 +1189,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
                        goto out_unmap;
                }
 
-               if (cc->is_khugepaged &&
-                   page_mapcount(page) > 1 &&
-                   ++shared > khugepaged_max_ptes_shared) {
-                       result = SCAN_EXCEED_SHARED_PTE;
-                       count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-                       goto out_unmap;
+               if (page_mapcount(page) > 1) {
+                       ++shared;
+                       if (cc->is_khugepaged &&
+                           shared > khugepaged_max_ptes_shared) {
+                               result = SCAN_EXCEED_SHARED_PTE;
+                               count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
+                               goto out_unmap;
+                       }
                }
 
                page = compound_head(page);
@@ -1924,8 +1932,9 @@ static int khugepaged_scan_file(struct mm_struct *mm, struct file *file,
                        continue;
 
                if (xa_is_value(page)) {
+                       ++swap;
                        if (cc->is_khugepaged &&
-                           ++swap > khugepaged_max_ptes_swap) {
+                           swap > khugepaged_max_ptes_swap) {
                                result = SCAN_EXCEED_SWAP_PTE;
                                count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
                                break;
@@ -1976,8 +1985,8 @@ static int khugepaged_scan_file(struct mm_struct *mm, struct file *file,
        rcu_read_unlock();
 
        if (result == SCAN_SUCCEED) {
-               if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none &&
-                   cc->is_khugepaged) {
+               if (cc->is_khugepaged &&
+                   present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
                        result = SCAN_EXCEED_NONE_PTE;
                        count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
                } else {