From 1b096e5ae9f7181c770d59c6895f23a76c63adee Mon Sep 17 00:00:00 2001 From: Vitaly Wool Date: Fri, 24 Feb 2017 14:57:20 -0800 Subject: [PATCH] z3fold: extend compaction function z3fold_compact_page() currently only handles the situation when there's a single middle chunk within the z3fold page. However it may be worth it to move middle chunk closer to either first or last chunk, whichever is there, if the gap between them is big enough. This patch adds the relevant code, using BIG_CHUNK_GAP define as a threshold for middle chunk to be worth moving. Link: http://lkml.kernel.org/r/20170131214334.c4f3eac9a477af0fa9a22c46@gmail.com Signed-off-by: Vitaly Wool Reviewed-by: Dan Streetman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/z3fold.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 98ab01f..be8b56e 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -268,6 +268,7 @@ static inline void *mchunk_memmove(struct z3fold_header *zhdr, zhdr->middle_chunks << CHUNK_SHIFT); } +#define BIG_CHUNK_GAP 3 /* Has to be called with lock held */ static int z3fold_compact_page(struct z3fold_header *zhdr) { @@ -286,8 +287,31 @@ static int z3fold_compact_page(struct z3fold_header *zhdr) zhdr->middle_chunks = 0; zhdr->start_middle = 0; zhdr->first_num++; + return 1; } - return 1; + + /* + * moving data is expensive, so let's only do that if + * there's substantial gain (at least BIG_CHUNK_GAP chunks) + */ + if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 && + zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >= + BIG_CHUNK_GAP) { + mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS); + zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS; + return 1; + } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 && + TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle + + zhdr->middle_chunks) >= + BIG_CHUNK_GAP) { + unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks - + zhdr->middle_chunks; + mchunk_memmove(zhdr, new_start); + zhdr->start_middle = new_start; + return 1; + } + + return 0; } /** -- 2.7.4