[RFC 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@xxxxxxxxxx>
---
 mm/pkram.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/pkram.c b/mm/pkram.c
index ef092aa5ce7a..416c3ca4411b 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -913,11 +913,21 @@ static int __pkram_save_page(struct pkram_stream *ps,
 {
 	struct pkram_link *link = ps->link;
 	struct pkram_obj *obj = ps->obj;
+	int order, align, align_cnt;
 	pkram_entry_t p;
-	int order;
+
+	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 || ps->entry_idx >= PKRAM_LINK_ENTRIES_MAX ||
-	    index != ps->next_index) {
+	    index != ps->next_index ||
+	    (IS_ALIGNED(index, align) &&
+	    (ps->entry_idx + align_cnt > PKRAM_LINK_ENTRIES_MAX))) {
 		struct page *link_page;
 
 		link_page = pkram_alloc_page((ps->gfp_mask & GFP_RECLAIM_MASK) |
-- 
2.13.3