[RFC PATCH 1/4] mm/swap.c: pre-sort pages in pagevec for pagevec_lru_move_fn

Alex Shi
2020-12-25T10:02:57Z

Pages in pagevec may have different lruvec, so we have to do relock in
function pagevec_lru_move_fn(), but a relock may cause current cpu wait
for long time on the same lock for spinlock fairness reason.

Before per memcg lru_lock, we have to bear the relock since the spinlock
is the only way to serialize page's memcg/lruvec. Now TestClearPageLRU
could be used to isolate pages exculsively, and stable the page's
lruvec/memcg. So it gives us a chance to sort the page's lruvec before
moving action in pagevec_lru_move_fn. Then we don't suffer from the
spinlock's fairness wait.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/swap.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 79 insertions(+), 13 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index c5363bdebe67..994641331bf7 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -201,29 +201,95 @@ int get_kernel_page(unsigned long start, int write, struct page **pages)
}
EXPORT_SYMBOL_GPL(get_kernel_page);

+/* Pratt's gaps for shell sort, https://en.wikipedia.org/wiki/Shellsort */
+static int gaps[] = { 6, 4, 3, 2, 1, 0};
+
+/* Shell sort pagevec[] on page's lruvec.*/
+static void shell_sort(struct pagevec *pvec, unsigned long *lvaddr)
+{
+ int g, i, j, n = pagevec_count(pvec);
+
+ for (g=0; gaps[g] > 0 && gaps[g] <= n/2; g++) {
+ int gap = gaps[g];
+
+ for (i = gap; i < n; i++) {
+ unsigned long tmp = lvaddr[i];
+ struct page *page = pvec->pages[i];
+
+ for (j = i - gap; j >= 0 && lvaddr[j] > tmp; j -= gap) {
+ lvaddr[j + gap] = lvaddr[j];
+ pvec->pages[j + gap] = pvec->pages[j];
+ }
+ lvaddr[j + gap] = tmp;
+ pvec->pages[j + gap] = page;
+ }
+ }
+}
+
+/* Get lru bit cleared page and their lruvec address, release the others */
+void sort_isopv(struct pagevec *pvec, struct pagevec *isopv,
+ unsigned long *lvaddr)
+{
+ int i, j;
+ struct pagevec busypv;
+
+ pagevec_init(&busypv);
+
+ for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+
+ pvec->pages[i] = NULL;
+
+ /* block memcg migration during page moving between lru */
+ if (!TestClearPageLRU(page)) {
+ pagevec_add(&busypv, page);
+ continue;
+ }
+ lvaddr[j++] = (unsigned long)
+ mem_cgroup_page_lruvec(page, page_pgdat(page));
+ pagevec_add(isopv, page);
+ }
+ pagevec_reinit(pvec);
+ if (pagevec_count(&busypv))
+ release_pages(busypv.pages, busypv.nr);
+
+ shell_sort(isopv, lvaddr);
+}
+
static void pagevec_lru_move_fn(struct pagevec *pvec,
void (*move_fn)(struct page *page, struct lruvec *lruvec))
{
- int i;
+ int i, n;
struct lruvec *lruvec = NULL;
unsigned long flags = 0;
+ unsigned long lvaddr[PAGEVEC_SIZE];
+ struct pagevec isopv;

- for (i = 0; i < pagevec_count(pvec); i++) {
- struct page *page = pvec->pages[i];
+ pagevec_init(&isopv);

- /* block memcg migration during page moving between lru */
- if (!TestClearPageLRU(page))
- continue;
+ sort_isopv(pvec, &isopv, lvaddr);

- lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
- (*move_fn)(page, lruvec);
+ n = pagevec_count(&isopv);
+ if (!n)
+ return;

- SetPageLRU(page);
+ lruvec = (struct lruvec *)lvaddr[0];
+ spin_lock_irqsave(&lruvec->lru_lock, flags);
+
+ for (i = 0; i < n; i++) {
+ /* lock new lruvec if lruvec changes, we have sorted them */
+ if (lruvec != (struct lruvec *)lvaddr[i]) {
+ spin_unlock_irqrestore(&lruvec->lru_lock, flags);
+ lruvec = (struct lruvec *)lvaddr[i];
+ spin_lock_irqsave(&lruvec->lru_lock, flags);
+ }
+
+ (*move_fn)(isopv.pages[i], lruvec);
+
+ SetPageLRU(isopv.pages[i]);
}
- if (lruvec)
- unlock_page_lruvec_irqrestore(lruvec, flags);
- release_pages(pvec->pages, pvec->nr);
- pagevec_reinit(pvec);
+ spin_unlock_irqrestore(&lruvec->lru_lock, flags);
+ release_pages(isopv.pages, isopv.nr);
}

static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
--
2.29.GIT