From: Vitaly Wool <vitalywool@xxxxxxxxx> Subject: 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@xxxxxxxxx Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx> Reviewed-by: Dan Streetman <ddstreet@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/z3fold.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff -puN mm/z3fold.c~z3fold-extend-compaction-function mm/z3fold.c --- a/mm/z3fold.c~z3fold-extend-compaction-function +++ a/mm/z3fold.c @@ -268,6 +268,7 @@ static inline void *mchunk_memmove(struc 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 z3 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; } /** _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
