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Subject[PATCH] xfs: reduce stack usage in xfs_bmap_btalloc()
Date
Hi David,

This patch reduces xfs_bmap_btalloc() stack usage by 50 bytes
by moving part of its body into a helper function.

This results in some variables not taking stack space in
xfs_bmap_btalloc() anymore.

The helper itself does not call anything stack-deep.
Stack-deep call to xfs_alloc_vextent() happen
in xfs_bmap_btalloc(), as before.

Compile tested only.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
--
vda
diff -urpN linux-2.6-xfs1/fs/xfs/xfs_bmap.c linux-2.6-xfs1.stk1/fs/xfs/xfs_bmap.c
--- linux-2.6-xfs1/fs/xfs/xfs_bmap.c 2008-04-22 04:16:25.000000000 +0200
+++ linux-2.6-xfs1.stk1/fs/xfs/xfs_bmap.c 2008-04-26 16:23:26.000000000 +0200
@@ -2648,26 +2648,18 @@ xfs_bmap_rtalloc(
}

STATIC int
-xfs_bmap_btalloc(
- xfs_bmalloca_t *ap) /* bmap alloc argument struct */
+xfs_bmap_btalloc_helper(
+ xfs_bmalloca_t *ap, /* bmap alloc argument struct */
+ xfs_alloc_arg_t *argsp,
+ xfs_extlen_t *blenp)
{
+#define args (*argsp)
+#define blen (*blenp)
xfs_mount_t *mp; /* mount point structure */
- xfs_alloctype_t atype = 0; /* type for allocation routines */
xfs_extlen_t align; /* minimum allocation alignment */
xfs_agnumber_t ag;
xfs_agnumber_t fb_agno; /* ag number of ap->firstblock */
- xfs_agnumber_t startag;
- xfs_alloc_arg_t args;
- xfs_extlen_t blen;
- xfs_extlen_t delta;
- xfs_extlen_t longest;
- xfs_extlen_t need;
- xfs_extlen_t nextminlen = 0;
- xfs_perag_t *pag;
int nullfb; /* true if ap->firstblock isn't set */
- int isaligned;
- int notinit;
- int tryagain;
int error;

mp = ap->ip->i_mount;
@@ -2705,7 +2697,6 @@ xfs_bmap_btalloc(
/*
* Normal allocation, done through xfs_alloc_vextent.
*/
- tryagain = isaligned = 0;
args.tp = ap->tp;
args.mp = mp;
args.fsbno = ap->rval;
@@ -2713,6 +2704,9 @@ xfs_bmap_btalloc(
args.firstblock = ap->firstblock;
blen = 0;
if (nullfb) {
+ xfs_agnumber_t startag;
+ int notinit;
+
if (ap->userdata && xfs_inode_is_filestream(ap->ip))
args.type = XFS_ALLOCTYPE_NEAR_BNO;
else
@@ -2732,6 +2726,8 @@ xfs_bmap_btalloc(
notinit = 0;
down_read(&mp->m_peraglock);
while (blen < ap->alen) {
+ xfs_perag_t *pag;
+
pag = &mp->m_perag[ag];
if (!pag->pagf_init &&
(error = xfs_alloc_pagf_init(mp, args.tp,
@@ -2743,6 +2739,10 @@ xfs_bmap_btalloc(
* See xfs_alloc_fix_freelist...
*/
if (pag->pagf_init) {
+ xfs_extlen_t need;
+ xfs_extlen_t delta;
+ xfs_extlen_t longest;
+
need = XFS_MIN_FREELIST_PAG(pag, mp);
delta = need > pag->pagf_flcount ?
need - pag->pagf_flcount : 0;
@@ -2838,6 +2838,33 @@ xfs_bmap_btalloc(
if ((args.mod = (xfs_extlen_t)(do_mod(ap->off, args.prod))))
args.mod = (xfs_extlen_t)(args.prod - args.mod);
}
+
+ return 0; /* no error */
+#undef args
+#undef blen
+}
+
+STATIC int
+xfs_bmap_btalloc(
+ xfs_bmalloca_t *ap) /* bmap alloc argument struct */
+{
+ xfs_mount_t *mp; /* mount point structure */
+ xfs_alloctype_t atype; /* type for allocation routines */
+ xfs_alloc_arg_t args;
+ xfs_extlen_t blen;
+ xfs_extlen_t nextminlen;
+ int nullfb; /* true if ap->firstblock isn't set */
+ int isaligned;
+ int tryagain;
+ int error;
+
+ error = xfs_bmap_btalloc_helper(ap, &args, &blen);
+ if (error)
+ return error;
+
+ mp = ap->ip->i_mount;
+ nullfb = ap->firstblock == NULLFSBLOCK;
+
/*
* If we are not low on available data blocks, and the
* underlying logical volume manager is a stripe, and
@@ -2847,10 +2874,13 @@ xfs_bmap_btalloc(
* is >= the stripe unit and the allocation offset is
* at the end of file.
*/
+ atype = 0;
+ nextminlen = 0;
+ tryagain = isaligned = 0;
if (!ap->low && ap->aeof) {
+ atype = args.type;
if (!ap->off) {
args.alignment = mp->m_dalign;
- atype = args.type;
isaligned = 1;
/*
* Adjust for alignment
@@ -2864,7 +2894,6 @@ xfs_bmap_btalloc(
* If it fails then do a near or start bno
* allocation with alignment turned on.
*/
- atype = args.type;
tryagain = 1;
args.type = XFS_ALLOCTYPE_THIS_BNO;
args.alignment = 1;
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