[RFC v2 43/43] PKRAM: improve index alignment of pkram_link entries

[Anthony Yznaga]

To take advantage of optimizations when adding pages to the page cache
via shmem_insert_pages(), improve the likelihood that the pages array
passed to shmem_insert_pages() starts on an aligned index.  Do this
when preserving pages by starting a new pkram_link page when the current
page is aligned and the next aligned page will not fit on the pkram_link
page.

Signed-off-by: Anthony Yznaga <anthony.yznaga at oracle.com>
---
 mm/pkram.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/mm/pkram.c b/mm/pkram.c
index b63b2a3958e7..3f43809c8a85 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -911,9 +911,20 @@ static int __pkram_save_page(struct pkram_access *pa, struct page *page,
 {
 	struct pkram_data_stream *pds = &pa->pds;
 	struct pkram_link *link = pds->link;
+	int align, align_cnt;
+
+	if (PageTransHuge(page)) {
+		align = 1 << (HPAGE_PMD_ORDER + XA_CHUNK_SHIFT - (HPAGE_PMD_ORDER % XA_CHUNK_SHIFT));
+		align_cnt = align >> HPAGE_PMD_ORDER;
+	} else {
+		align = XA_CHUNK_SIZE;
+		align_cnt = XA_CHUNK_SIZE;
+	}
 
 	if (!link || pds->entry_idx >= PKRAM_LINK_ENTRIES_MAX ||
-	    index != pa->pages.next_index) {
+	    index != pa->pages.next_index ||
+	    (IS_ALIGNED(index, align) &&
+	    (pds->entry_idx + align_cnt > PKRAM_LINK_ENTRIES_MAX))) {
 		link = pkram_new_link(pds, pa->ps->gfp_mask);
 		if (!link)
 			return -ENOMEM;
-- 
1.8.3.1