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[PATCH] xfs: factor duplicate code in xfs_alloc_ag_vextent_near into a h

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: factor duplicate code in xfs_alloc_ag_vextent_near into a helper
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Fri, 10 Dec 2010 10:04:11 -0500
User-agent: Mutt/1.5.21 (2010-09-15)
Add a new xfs_alloc_find_best_extent that does a forward/backward search
in the allocation btree.  That code previously was existed two times in
xfs_alloc_ag_vextent_near, once for each search direction.

Based on an earlier patch from Dave Chinner.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c 2010-12-10 09:50:07.681023471 +0100
+++ xfs/fs/xfs/xfs_alloc.c      2010-12-10 09:51:32.874005592 +0100
@@ -665,6 +665,95 @@ error0:
 }
 
 /*
+ * Search the btree in a given direction via the search cursor and compare
+ * the records found against the good extent we've already found.
+ */
+STATIC int
+xfs_alloc_find_best_extent(
+       struct xfs_alloc_arg    *args,  /* allocation argument structure */
+       struct xfs_btree_cur    **gcur, /* good cursor */
+       struct xfs_btree_cur    **scur, /* searching cursor */
+       xfs_agblock_t           gdiff,  /* difference for search comparison */
+       xfs_agblock_t           *sbno,  /* extent found by search */
+       xfs_extlen_t            *slen,
+       xfs_extlen_t            *slena, /* aligned length */
+       int                     dir)    /* 0 = search right, 1 = search left */
+{
+       xfs_agblock_t           bno;
+       xfs_agblock_t           new;
+       xfs_agblock_t           sdiff;
+       int                     error;
+       int                     i;
+
+       /* The good extent is perfect, no need to  search. */
+       if (!gdiff)
+               goto out_use_good;
+
+       /*
+        * Look until we find a better one, run out of space or run off the end.
+        */
+       do {
+               error = xfs_alloc_get_rec(*scur, sbno, slen, &i);
+               if (error)
+                       goto error0;
+               XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
+               xfs_alloc_compute_aligned(*sbno, *slen, args->alignment,
+                                         args->minlen, &bno, slena);
+
+               /*
+                * The good extent is closer than this one.
+                */
+               if (!dir) {
+                       if (bno >= args->agbno + gdiff)
+                               goto out_use_good;
+               } else {
+                       if (bno <= args->agbno - gdiff)
+                               goto out_use_good;
+               }
+
+               /*
+                * Same distance, compare length and pick the best.
+                */
+               if (*slena >= args->minlen) {
+                       args->len = XFS_EXTLEN_MIN(*slena, args->maxlen);
+                       xfs_alloc_fix_len(args);
+
+                       sdiff = xfs_alloc_compute_diff(args->agbno, args->len,
+                                                      args->alignment, *sbno,
+                                                      *slen, &new);
+
+                       /*
+                        * Choose closer size and invalidate other cursor.
+                        */
+                       if (sdiff < gdiff)
+                               goto out_use_search;
+                       goto out_use_good;
+               }
+
+               if (!dir)
+                       error = xfs_btree_increment(*scur, 0, &i);
+               else
+                       error = xfs_btree_decrement(*scur, 0, &i);
+               if (error)
+                       goto error0;
+       } while (i);
+
+out_use_good:
+       xfs_btree_del_cursor(*scur, XFS_BTREE_NOERROR);
+       *scur = NULL;
+       return 0;
+
+out_use_search:
+       xfs_btree_del_cursor(*gcur, XFS_BTREE_NOERROR);
+       *gcur = NULL;
+       return 0;
+
+error0:
+       /* caller invalidates cursors */
+       return error;
+}
+
+/*
  * Allocate a variable extent near bno in the allocation group agno.
  * Extent's length (returned in len) will be between minlen and maxlen,
  * and of the form k * prod + mod unless there's nothing that large.
@@ -931,203 +1020,45 @@ xfs_alloc_ag_vextent_near(
                        }
                }
        } while (bno_cur_lt || bno_cur_gt);
+
        /*
         * Got both cursors still active, need to find better entry.
         */
        if (bno_cur_lt && bno_cur_gt) {
-               /*
-                * Left side is long enough, look for a right side entry.
-                */
                if (ltlena >= args->minlen) {
                        /*
-                        * Fix up the length.
+                        * Left side is good, look for a right side entry.
                         */
                        args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
                        xfs_alloc_fix_len(args);
-                       rlen = args->len;
-                       ltdiff = xfs_alloc_compute_diff(args->agbno, rlen,
+                       ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                args->alignment, ltbno, ltlen, &ltnew);
+
+                       error = xfs_alloc_find_best_extent(args,
+                                               &bno_cur_lt, &bno_cur_gt,
+                                               ltdiff, &gtbno, &gtlen, &gtlena,
+                                               0 /* search right */);
+               } else {
+                       ASSERT(gtlena >= args->minlen);
+
                        /*
-                        * Not perfect.
-                        */
-                       if (ltdiff) {
-                               /*
-                                * Look until we find a better one, run out of
-                                * space, or run off the end.
-                                */
-                               while (bno_cur_lt && bno_cur_gt) {
-                                       if ((error = xfs_alloc_get_rec(
-                                                       bno_cur_gt, &gtbno,
-                                                       &gtlen, &i)))
-                                               goto error0;
-                                       XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
-                                       xfs_alloc_compute_aligned(gtbno, gtlen,
-                                               args->alignment, args->minlen,
-                                               &gtbnoa, &gtlena);
-                                       /*
-                                        * The left one is clearly better.
-                                        */
-                                       if (gtbnoa >= args->agbno + ltdiff) {
-                                               xfs_btree_del_cursor(
-                                                       bno_cur_gt,
-                                                       XFS_BTREE_NOERROR);
-                                               bno_cur_gt = NULL;
-                                               break;
-                                       }
-                                       /*
-                                        * If we reach a big enough entry,
-                                        * compare the two and pick the best.
-                                        */
-                                       if (gtlena >= args->minlen) {
-                                               args->len =
-                                                       XFS_EXTLEN_MIN(gtlena,
-                                                               args->maxlen);
-                                               xfs_alloc_fix_len(args);
-                                               rlen = args->len;
-                                               gtdiff = xfs_alloc_compute_diff(
-                                                       args->agbno, rlen,
-                                                       args->alignment,
-                                                       gtbno, gtlen, &gtnew);
-                                               /*
-                                                * Right side is better.
-                                                */
-                                               if (gtdiff < ltdiff) {
-                                                       xfs_btree_del_cursor(
-                                                               bno_cur_lt,
-                                                               
XFS_BTREE_NOERROR);
-                                                       bno_cur_lt = NULL;
-                                               }
-                                               /*
-                                                * Left side is better.
-                                                */
-                                               else {
-                                                       xfs_btree_del_cursor(
-                                                               bno_cur_gt,
-                                                               
XFS_BTREE_NOERROR);
-                                                       bno_cur_gt = NULL;
-                                               }
-                                               break;
-                                       }
-                                       /*
-                                        * Fell off the right end.
-                                        */
-                                       if ((error = xfs_btree_increment(
-                                                       bno_cur_gt, 0, &i)))
-                                               goto error0;
-                                       if (!i) {
-                                               xfs_btree_del_cursor(
-                                                       bno_cur_gt,
-                                                       XFS_BTREE_NOERROR);
-                                               bno_cur_gt = NULL;
-                                               break;
-                                       }
-                               }
-                       }
-                       /*
-                        * The left side is perfect, trash the right side.
-                        */
-                       else {
-                               xfs_btree_del_cursor(bno_cur_gt,
-                                                    XFS_BTREE_NOERROR);
-                               bno_cur_gt = NULL;
-                       }
-               }
-               /*
-                * It's the right side that was found first, look left.
-                */
-               else {
-                       /*
-                        * Fix up the length.
+                        * Right side is good, look for a left side entry.
                         */
                        args->len = XFS_EXTLEN_MIN(gtlena, args->maxlen);
                        xfs_alloc_fix_len(args);
-                       rlen = args->len;
-                       gtdiff = xfs_alloc_compute_diff(args->agbno, rlen,
+                       gtdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                args->alignment, gtbno, gtlen, &gtnew);
-                       /*
-                        * Right side entry isn't perfect.
-                        */
-                       if (gtdiff) {
-                               /*
-                                * Look until we find a better one, run out of
-                                * space, or run off the end.
-                                */
-                               while (bno_cur_lt && bno_cur_gt) {
-                                       if ((error = xfs_alloc_get_rec(
-                                                       bno_cur_lt, &ltbno,
-                                                       &ltlen, &i)))
-                                               goto error0;
-                                       XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
-                                       xfs_alloc_compute_aligned(ltbno, ltlen,
-                                               args->alignment, args->minlen,
-                                               &ltbnoa, &ltlena);
-                                       /*
-                                        * The right one is clearly better.
-                                        */
-                                       if (ltbnoa <= args->agbno - gtdiff) {
-                                               xfs_btree_del_cursor(
-                                                       bno_cur_lt,
-                                                       XFS_BTREE_NOERROR);
-                                               bno_cur_lt = NULL;
-                                               break;
-                                       }
-                                       /*
-                                        * If we reach a big enough entry,
-                                        * compare the two and pick the best.
-                                        */
-                                       if (ltlena >= args->minlen) {
-                                               args->len = XFS_EXTLEN_MIN(
-                                                       ltlena, args->maxlen);
-                                               xfs_alloc_fix_len(args);
-                                               rlen = args->len;
-                                               ltdiff = xfs_alloc_compute_diff(
-                                                       args->agbno, rlen,
-                                                       args->alignment,
-                                                       ltbno, ltlen, &ltnew);
-                                               /*
-                                                * Left side is better.
-                                                */
-                                               if (ltdiff < gtdiff) {
-                                                       xfs_btree_del_cursor(
-                                                               bno_cur_gt,
-                                                               
XFS_BTREE_NOERROR);
-                                                       bno_cur_gt = NULL;
-                                               }
-                                               /*
-                                                * Right side is better.
-                                                */
-                                               else {
-                                                       xfs_btree_del_cursor(
-                                                               bno_cur_lt,
-                                                               
XFS_BTREE_NOERROR);
-                                                       bno_cur_lt = NULL;
-                                               }
-                                               break;
-                                       }
-                                       /*
-                                        * Fell off the left end.
-                                        */
-                                       if ((error = xfs_btree_decrement(
-                                                       bno_cur_lt, 0, &i)))
-                                               goto error0;
-                                       if (!i) {
-                                               xfs_btree_del_cursor(bno_cur_lt,
-                                                       XFS_BTREE_NOERROR);
-                                               bno_cur_lt = NULL;
-                                               break;
-                                       }
-                               }
-                       }
-                       /*
-                        * The right side is perfect, trash the left side.
-                        */
-                       else {
-                               xfs_btree_del_cursor(bno_cur_lt,
-                                       XFS_BTREE_NOERROR);
-                               bno_cur_lt = NULL;
-                       }
+
+                       error = xfs_alloc_find_best_extent(args,
+                                               &bno_cur_gt, &bno_cur_lt,
+                                               gtdiff, &ltbno, &ltlen, &ltlena,
+                                               1 /* search left */);
                }
+
+               if (error)
+                       goto error0;
        }
+
        /*
         * If we couldn't get anything, give up.
         */
@@ -1136,6 +1067,7 @@ xfs_alloc_ag_vextent_near(
                args->agbno = NULLAGBLOCK;
                return 0;
        }
+
        /*
         * At this point we have selected a freespace entry, either to the
         * left or to the right.  If it's on the right, copy all the
@@ -1152,6 +1084,7 @@ xfs_alloc_ag_vextent_near(
                j = 1;
        } else
                j = 0;
+
        /*
         * Fix up the length and compute the useful address.
         */

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