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[PATCH 1/4] xfs: add online discard support

To: xfs@xxxxxxxxxxx
Subject: [PATCH 1/4] xfs: add online discard support
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 04 May 2011 14:55:14 -0400
References: <20110504185513.136746538@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: quilt/0.48-1
Now that we have reliably tracking of deleted extents in a transaction
we can easily implement "online" discard support which calls
blkdev_issue_discard once a transaction commits.

The actual discard is a two stage operation as we first have to mark
the busy extent as not available for reuse before we can start the
actual discard.  Note that we don't bother supporting discard for
the non-delaylog mode.

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

Index: xfs/fs/xfs/linux-2.6/xfs_super.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_super.c       2011-05-04 20:44:30.466422727 
+0200
+++ xfs/fs/xfs/linux-2.6/xfs_super.c    2011-05-04 20:45:06.302895250 +0200
@@ -112,6 +112,8 @@ mempool_t *xfs_ioend_pool;
 #define MNTOPT_QUOTANOENF  "qnoenforce"        /* same as uqnoenforce */
 #define MNTOPT_DELAYLOG   "delaylog"   /* Delayed loging enabled */
 #define MNTOPT_NODELAYLOG "nodelaylog" /* Delayed loging disabled */
+#define MNTOPT_DISCARD "discard"       /* Discard unused blocks */
+#define MNTOPT_NODISCARD "nodiscard"   /* Do not discard unused blocks */
 
 /*
  * Table driven mount option parser.
@@ -355,6 +357,10 @@ xfs_parseargs(
                        mp->m_flags |= XFS_MOUNT_DELAYLOG;
                } else if (!strcmp(this_char, MNTOPT_NODELAYLOG)) {
                        mp->m_flags &= ~XFS_MOUNT_DELAYLOG;
+               } else if (!strcmp(this_char, MNTOPT_DISCARD)) {
+                       mp->m_flags |= XFS_MOUNT_DISCARD;
+               } else if (!strcmp(this_char, MNTOPT_NODISCARD)) {
+                       mp->m_flags &= ~XFS_MOUNT_DISCARD;
                } else if (!strcmp(this_char, "ihashsize")) {
                        xfs_warn(mp,
        "ihashsize no longer used, option is deprecated.");
@@ -488,6 +494,7 @@ xfs_showargs(
                { XFS_MOUNT_FILESTREAMS,        "," MNTOPT_FILESTREAM },
                { XFS_MOUNT_GRPID,              "," MNTOPT_GRPID },
                { XFS_MOUNT_DELAYLOG,           "," MNTOPT_DELAYLOG },
+               { XFS_MOUNT_DISCARD,            "," MNTOPT_DISCARD },
                { 0, NULL }
        };
        static struct proc_xfs_info xfs_info_unset[] = {
Index: xfs/fs/xfs/xfs_mount.h
===================================================================
--- xfs.orig/fs/xfs/xfs_mount.h 2011-05-04 20:44:30.356423323 +0200
+++ xfs/fs/xfs/xfs_mount.h      2011-05-04 20:45:06.302895250 +0200
@@ -224,6 +224,7 @@ typedef struct xfs_mount {
 #define XFS_MOUNT_FS_SHUTDOWN  (1ULL << 4)     /* atomic stop of all filesystem
                                                   operations, typically for
                                                   disk errors in metadata */
+#define XFS_MOUNT_DISCARD      (1ULL << 5)     /* discard unused blocks */
 #define XFS_MOUNT_RETERR       (1ULL << 6)     /* return alignment errors to
                                                   user */
 #define XFS_MOUNT_NOALIGN      (1ULL << 7)     /* turn off stripe alignment
Index: xfs/fs/xfs/xfs_log_cil.c
===================================================================
--- xfs.orig/fs/xfs/xfs_log_cil.c       2011-05-04 20:44:30.369756584 +0200
+++ xfs/fs/xfs/xfs_log_cil.c    2011-05-04 20:45:06.302895250 +0200
@@ -29,6 +29,7 @@
 #include "xfs_mount.h"
 #include "xfs_error.h"
 #include "xfs_alloc.h"
+#include "xfs_discard.h"
 
 /*
  * Perform initial CIL structure initialisation. If the CIL is not
@@ -361,18 +362,28 @@ xlog_cil_committed(
        int     abort)
 {
        struct xfs_cil_ctx      *ctx = args;
+       struct xfs_mount        *mp = ctx->cil->xc_log->l_mp;
 
        xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
                                        ctx->start_lsn, abort);
 
        xfs_alloc_busy_sort(&ctx->busy_extents);
-       xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, &ctx->busy_extents);
+       xfs_alloc_busy_clear(mp, &ctx->busy_extents,
+                            (mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
 
        spin_lock(&ctx->cil->xc_cil_lock);
        list_del(&ctx->committing);
        spin_unlock(&ctx->cil->xc_cil_lock);
 
        xlog_cil_free_logvec(ctx->lv_chain);
+
+       if (!list_empty(&ctx->busy_extents)) {
+               ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);
+
+               xfs_discard_extents(mp, &ctx->busy_extents);
+               xfs_alloc_busy_clear(mp, &ctx->busy_extents, false);
+       }
+
        kmem_free(ctx);
 }
 
Index: xfs/fs/xfs/linux-2.6/xfs_discard.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_discard.c     2011-05-04 20:44:30.329756801 
+0200
+++ xfs/fs/xfs/linux-2.6/xfs_discard.c  2011-05-04 20:45:06.306228566 +0200
@@ -191,3 +191,32 @@ xfs_ioc_trim(
                return -XFS_ERROR(EFAULT);
        return 0;
 }
+
+int
+xfs_discard_extents(
+       struct xfs_mount        *mp,
+       struct list_head        *list)
+{
+       struct xfs_busy_extent  *busyp;
+       int                     error = 0;
+
+       list_for_each_entry(busyp, list, list) {
+               trace_xfs_discard_extent(mp, busyp->agno, busyp->bno,
+                                        busyp->length);
+
+               error = -blkdev_issue_discard(mp->m_ddev_targp->bt_bdev,
+                               XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno),
+                               XFS_FSB_TO_BB(mp, busyp->length),
+                               GFP_NOFS, 0);
+               if (error && error != EOPNOTSUPP) {
+                       xfs_info(mp,
+        "discard failed for extent [0x%llu,%u], error %d",
+                                (unsigned long long)busyp->bno,
+                                busyp->length,
+                                error);
+                       return error;
+               }
+       }
+
+       return 0;
+}
Index: xfs/fs/xfs/linux-2.6/xfs_discard.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_discard.h     2011-05-04 20:44:30.343090061 
+0200
+++ xfs/fs/xfs/linux-2.6/xfs_discard.h  2011-05-04 20:45:06.306228566 +0200
@@ -2,7 +2,9 @@
 #define XFS_DISCARD_H 1
 
 struct fstrim_range;
+struct list_head;
 
 extern int     xfs_ioc_trim(struct xfs_mount *, struct fstrim_range __user *);
+extern int     xfs_discard_extents(struct xfs_mount *, struct list_head *);
 
 #endif /* XFS_DISCARD_H */
Index: xfs/fs/xfs/xfs_ag.h
===================================================================
--- xfs.orig/fs/xfs/xfs_ag.h    2011-05-04 20:44:30.376423214 +0200
+++ xfs/fs/xfs/xfs_ag.h 2011-05-04 20:45:11.406200936 +0200
@@ -187,6 +187,8 @@ struct xfs_busy_extent {
        xfs_agnumber_t  agno;
        xfs_agblock_t   bno;
        xfs_extlen_t    length;
+       unsigned int    flags;
+#define XFS_ALLOC_BUSY_DISCARDED       0x01    /* undergoing a discard op. */
 };
 
 /*
Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c 2011-05-04 20:44:30.386423159 +0200
+++ xfs/fs/xfs/xfs_alloc.c      2011-05-04 20:45:11.432867459 +0200
@@ -2610,6 +2610,18 @@ xfs_alloc_busy_update_extent(
        xfs_agblock_t           bend = bbno + busyp->length;
 
        /*
+        * This extent is currently beeing discard.  Give the thread
+        * performing the discard a chance to mark the extent unbusy
+        * and retry.
+        */
+       if (busyp->flags & XFS_ALLOC_BUSY_DISCARDED) {
+               spin_unlock(&pag->pagb_lock);
+               delay(1);
+               spin_lock(&pag->pagb_lock);
+               return false;
+       }
+
+       /*
         * If there is a busy extent overlapping a user allocation, we have
         * no choice but to force the log and retry the search.
         *
@@ -2814,7 +2826,8 @@ restart:
                 * If this is a metadata allocation, try to reuse the busy
                 * extent instead of trimming the allocation.
                 */
-               if (!args->userdata) {
+               if (!args->userdata &&
+                   !(busyp->flags & XFS_ALLOC_BUSY_DISCARDED)) {
                        if (!xfs_alloc_busy_update_extent(args->mp, args->pag,
                                                          busyp, fbno, flen,
                                                          false))
@@ -2980,10 +2993,16 @@ xfs_alloc_busy_clear_one(
        kmem_free(busyp);
 }
 
+/*
+ * Remove all extents on the passed in list from the busy extents tree.
+ * If do_discard is set skip extents that need to be discarded, and mark
+ * these as undergoing a discard operation instead.
+ */
 void
 xfs_alloc_busy_clear(
        struct xfs_mount        *mp,
-       struct list_head        *list)
+       struct list_head        *list,
+       bool                    do_discard)
 {
        struct xfs_busy_extent  *busyp, *n;
        struct xfs_perag        *pag = NULL;
@@ -3000,7 +3019,10 @@ xfs_alloc_busy_clear(
                        agno = busyp->agno;
                }
 
-               xfs_alloc_busy_clear_one(mp, pag, busyp);
+               if (do_discard && busyp->length)
+                       busyp->flags = XFS_ALLOC_BUSY_DISCARDED;
+               else
+                       xfs_alloc_busy_clear_one(mp, pag, busyp);
        }
 
        if (pag) {
Index: xfs/Documentation/filesystems/xfs.txt
===================================================================
--- xfs.orig/Documentation/filesystems/xfs.txt  2011-05-04 20:44:30.409756366 
+0200
+++ xfs/Documentation/filesystems/xfs.txt       2011-05-04 20:45:06.306228566 
+0200
@@ -39,6 +39,12 @@ When mounting an XFS filesystem, the fol
        drive level write caching to be enabled, for devices that
        support write barriers.
 
+  discard
+       Issue command to let the block device reclaim space freed by the
+       filesystem.  This is useful for SSD devices, thinly provisioned
+       LUNs and virtual machine images, but may have a performance
+       impact.
+
   dmapi
        Enable the DMAPI (Data Management API) event callouts.
        Use with the "mtpt" option.
Index: xfs/fs/xfs/xfs_alloc.h
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.h 2011-05-04 20:44:30.393089791 +0200
+++ xfs/fs/xfs/xfs_alloc.h      2011-05-04 20:45:11.452867351 +0200
@@ -140,7 +140,8 @@ xfs_alloc_busy_insert(struct xfs_trans *
        xfs_agblock_t bno, xfs_extlen_t len);
 
 void
-xfs_alloc_busy_clear(struct xfs_mount *mp, struct list_head *list);
+xfs_alloc_busy_clear(struct xfs_mount *mp, struct list_head *list,
+       bool do_discard);
 
 int
 xfs_alloc_busy_search(struct xfs_mount *mp, xfs_agnumber_t agno,
Index: xfs/fs/xfs/xfs_trans.c
===================================================================
--- xfs.orig/fs/xfs/xfs_trans.c 2011-05-04 20:44:30.399756421 +0200
+++ xfs/fs/xfs/xfs_trans.c      2011-05-04 20:45:06.306228566 +0200
@@ -609,7 +609,7 @@ xfs_trans_free(
        struct xfs_trans        *tp)
 {
        xfs_alloc_busy_sort(&tp->t_busy);
-       xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy);
+       xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy, false);
 
        atomic_dec(&tp->t_mountp->m_active_trans);
        xfs_trans_free_dqinfo(tp);

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