Commit 4d633062 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: introduce bvec_nth_page() 



Single-page bvec can often be seen in small BS workloads, so
introduce bvec_nth_page() for avoiding to call nth_page() unnecessarily,
which looks not cheap.

Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 81214bab

block/blk-merge.c

+1 −1
Original line number Diff line number Diff line
@@ -483,7 +483,7 @@ static unsigned blk_bvec_map_sg(struct request_queue *q, 


		offset = (total + bvec->bv_offset) % PAGE_SIZE;

		idx = (total + bvec->bv_offset) / PAGE_SIZE;

		pg = nth_page(bvec->bv_page, idx);

		pg = bvec_nth_page(bvec->bv_page, idx);



		sg_set_page(*sg, pg, seg_size, offset);

include/linux/bvec.h

+8 −3
Original line number Diff line number Diff line
@@ -51,6 +51,11 @@ struct bvec_iter_all { 
	unsigned	done;

};



static inline struct page *bvec_nth_page(struct page *page, int idx)

{

	return idx == 0 ? page : nth_page(page, idx);

}



/*

 * various member access, note that bio_data should of course not be used

 * on highmem page vectors
@@ -87,7 +92,7 @@ struct bvec_iter_all { 
	      PAGE_SIZE - bvec_iter_offset((bvec), (iter)))



#define bvec_iter_page(bvec, iter)				\

	nth_page(mp_bvec_iter_page((bvec), (iter)),		\

	bvec_nth_page(mp_bvec_iter_page((bvec), (iter)),		\

		      mp_bvec_iter_page_idx((bvec), (iter)))



#define bvec_iter_bvec(bvec, iter)				\
@@ -171,7 +176,7 @@ static inline void mp_bvec_last_segment(const struct bio_vec *bvec, 
	unsigned total = bvec->bv_offset + bvec->bv_len;

	unsigned last_page = (total - 1) / PAGE_SIZE;



	seg->bv_page = nth_page(bvec->bv_page, last_page);

	seg->bv_page = bvec_nth_page(bvec->bv_page, last_page);



	/* the whole segment is inside the last page */

	if (bvec->bv_offset >= last_page * PAGE_SIZE) {