[PATCH] pktcdvd: Reduce stack usage

Reduce stack usage in the pkt_start_write() function.  Even though it's not
currently a real problem, the pages and offsets arrays can be eliminated,
which saves approximately 1000 bytes of stack space.

Signed-off-by: Peter Osterlund <petero2@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 89d8fe014efaeace444a0a6c89dbe97b48a83260..93e44d0292ab7aa56c04c4552ef2607bb6add19b 100644 (file)
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -645,7 +645,7 @@ static void pkt_copy_bio_data(struct bio *src_bio, int seg, int offs, struct pag
  * b) The data can be used as cache to avoid read requests if we receive a
  *    new write request for the same zone.
  */
-static void pkt_make_local_copy(struct packet_data *pkt, struct page **pages, int *offsets)
+static void pkt_make_local_copy(struct packet_data *pkt, struct bio_vec *bvec)
 {
        int f, p, offs;
 
@@ -653,15 +653,15 @@ static void pkt_make_local_copy(struct packet_data *pkt, struct page **pages, in
        p = 0;
        offs = 0;
        for (f = 0; f < pkt->frames; f++) {
-               if (pages[f] != pkt->pages[p]) {
-                       void *vfrom = kmap_atomic(pages[f], KM_USER0) + offsets[f];
+               if (bvec[f].bv_page != pkt->pages[p]) {
+                       void *vfrom = kmap_atomic(bvec[f].bv_page, KM_USER0) + bvec[f].bv_offset;
                        void *vto = page_address(pkt->pages[p]) + offs;
                        memcpy(vto, vfrom, CD_FRAMESIZE);
                        kunmap_atomic(vfrom, KM_USER0);
-                       pages[f] = pkt->pages[p];
-                       offsets[f] = offs;
+                       bvec[f].bv_page = pkt->pages[p];
+                       bvec[f].bv_offset = offs;
                } else {
-                       BUG_ON(offsets[f] != offs);
+                       BUG_ON(bvec[f].bv_offset != offs);
                }
                offs += CD_FRAMESIZE;
                if (offs >= PAGE_SIZE) {
@@ -991,18 +991,17 @@ try_next_bio:
 static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
 {
        struct bio *bio;
-       struct page *pages[PACKET_MAX_SIZE];
-       int offsets[PACKET_MAX_SIZE];
        int f;
        int frames_write;
+       struct bio_vec *bvec = pkt->w_bio->bi_io_vec;
 
        for (f = 0; f < pkt->frames; f++) {
-               pages[f] = pkt->pages[(f * CD_FRAMESIZE) / PAGE_SIZE];
-               offsets[f] = (f * CD_FRAMESIZE) % PAGE_SIZE;
+               bvec[f].bv_page = pkt->pages[(f * CD_FRAMESIZE) / PAGE_SIZE];
+               bvec[f].bv_offset = (f * CD_FRAMESIZE) % PAGE_SIZE;
        }
 
        /*
-        * Fill-in pages[] and offsets[] with data from orig_bios.
+        * Fill-in bvec with data from orig_bios.
         */
        frames_write = 0;
        spin_lock(&pkt->lock);
@@ -1024,11 +1023,11 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
                        }
 
                        if (src_bvl->bv_len - src_offs >= CD_FRAMESIZE) {
-                               pages[f] = src_bvl->bv_page;
-                               offsets[f] = src_bvl->bv_offset + src_offs;
+                               bvec[f].bv_page = src_bvl->bv_page;
+                               bvec[f].bv_offset = src_bvl->bv_offset + src_offs;
                        } else {
                                pkt_copy_bio_data(bio, segment, src_offs,
-                                                 pages[f], offsets[f]);
+                                                 bvec[f].bv_page, bvec[f].bv_offset);
                        }
                        src_offs += CD_FRAMESIZE;
                        frames_write++;
@@ -1042,7 +1041,7 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
        BUG_ON(frames_write != pkt->write_size);
 
        if (test_bit(PACKET_MERGE_SEGS, &pd->flags) || (pkt->write_size < pkt->frames)) {
-               pkt_make_local_copy(pkt, pages, offsets);
+               pkt_make_local_copy(pkt, bvec);
                pkt->cache_valid = 1;
        } else {
                pkt->cache_valid = 0;
@@ -1055,17 +1054,9 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
        pkt->w_bio->bi_bdev = pd->bdev;
        pkt->w_bio->bi_end_io = pkt_end_io_packet_write;
        pkt->w_bio->bi_private = pkt;
-       for (f = 0; f < pkt->frames; f++) {
-               if ((f + 1 < pkt->frames) && (pages[f + 1] == pages[f]) &&
-                   (offsets[f + 1] = offsets[f] + CD_FRAMESIZE)) {
-                       if (!bio_add_page(pkt->w_bio, pages[f], CD_FRAMESIZE * 2, offsets[f]))
-                               BUG();
-                       f++;
-               } else {
-                       if (!bio_add_page(pkt->w_bio, pages[f], CD_FRAMESIZE, offsets[f]))
-                               BUG();
-               }
-       }
+       for (f = 0; f < pkt->frames; f++)
+               if (!bio_add_page(pkt->w_bio, bvec[f].bv_page, CD_FRAMESIZE, bvec[f].bv_offset))
+                       BUG();
        VPRINTK("pktcdvd: vcnt=%d\n", pkt->w_bio->bi_vcnt);
 
        atomic_set(&pkt->io_wait, 1);