[PATCH -mm] fs/bio.c: tweaks

[PATCH -mm] fs/bio.c: tweaks

[Andreas Mohr]

Calculate a variable in bvec_alloc_bs() only once needed, not earlier
(bio.o down from 18408 to 18376 Bytes, 32 Bytes saved, probably due to
data locality improvements).
Init variable idx to silence a gcc warning which already existed in the
unmodified original base file (bvec_alloc_bs() handles idx
correctly, so there's no need for the warning):
fs/bio.c: In function `bio_alloc_bioset':
fs/bio.c:169: warning: `idx' may be used uninitialized in this function
Inline bio_set_map_data() since it's only called once.

Compile-tested and run-tested on 2.6.18-rc4-mm3.


Signed-off-by: Andreas Mohr <andi@lisas.de>


--- linux-2.6.18-rc4-mm3.orig/fs/bio.c	2006-09-04 23:38:46.000000000 +0200
+++ linux-2.6.18-rc4-mm3/fs/bio.c	2006-09-08 22:07:54.000000000 +0200
@@ -79,7 +79,6 @@
 static inline struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx, struct bio_set *bs)
 {
 	struct bio_vec *bvl;
-	struct biovec_slab *bp;
 
 	/*
 	 * see comment near bvec_array define!
@@ -98,10 +97,12 @@
 	 * idx now points to the pool we want to allocate from
 	 */
 
-	bp = bvec_slabs + *idx;
 	bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
-	if (bvl)
+	if (bvl) {
+		struct biovec_slab *bp = bvec_slabs + *idx;
+
 		memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));
+	}
 
 	return bvl;
 }
@@ -166,7 +167,7 @@
 
 		bio_init(bio);
 		if (likely(nr_iovecs)) {
-			unsigned long idx;
+			unsigned long idx = 0; /* shut up gcc */
 
 			bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
 			if (unlikely(!bvl)) {
@@ -455,7 +456,7 @@
 	void __user *userptr;
 };
 
-static void bio_set_map_data(struct bio_map_data *bmd, struct bio *bio)
+static inline void bio_set_map_data(struct bio_map_data *bmd, struct bio *bio)
 {
 	memcpy(bmd->iovecs, bio->bi_io_vec, sizeof(struct bio_vec) * bio->bi_vcnt);
 	bio->bi_private = bmd;

Re: [PATCH -mm] fs/bio.c: tweaks

[Andrew Morton]

On Thu, 31 Aug 2006 23:20:23 +0200
Andreas Mohr <andi@rhlx01.fht-esslingen.de> wrote:

> Calculate a variable in bvec_alloc_bs() only once needed, not earlier
> (bio.o down from 18408 to 18376 Bytes, 32 Bytes saved, probably due to
> data locality improvements).

OK, I spose.

> Init variable idx to silence a gcc warning which already existed in the
> unmodified original base file (bvec_alloc_bs() handles idx
> correctly, so there's no need for the warning):
> fs/bio.c: In function `bio_alloc_bioset':
> fs/bio.c:169: warning: `idx' may be used uninitialized in this function

I'm heartily sick of that one too.

> Inline bio_set_map_data() since it's only called once.

Is OK, gcc will take care of that.