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[PATCH 5/6] xfs: add online discard support

To: xfs@xxxxxxxxxxx
Subject: [PATCH 5/6] xfs: add online discard support
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 22 Mar 2011 15:55:55 -0400
References: <20110322195550.260682574@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.  While that would be possible with this patch
performance is awfull, and the optimization in the next patch won't
work as easily.

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       2011-03-21 14:51:40.806473979 
+0100
+++ xfs/fs/xfs/linux-2.6/xfs_super.c    2011-03-21 14:51:41.437974814 +0100
@@ -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.
@@ -356,6 +358,10 @@ 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.");
@@ -489,6 +495,7 @@ 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 2011-03-21 14:47:03.630474095 +0100
+++ xfs/fs/xfs/xfs_mount.h      2011-03-21 14:51:41.437974814 +0100
@@ -227,6 +227,7 @@ 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       2011-03-21 14:47:03.638475274 +0100
+++ xfs/fs/xfs/xfs_log_cil.c    2011-03-21 14:51:41.441975564 +0100
@@ -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
@@ -361,13 +362,17 @@ xlog_cil_committed(
        int     abort)
 {
        struct xfs_cil_ctx      *ctx = args;
+       struct xfs_mount        *mp = ctx->cil->xc_log->l_mp;
        struct xfs_busy_extent  *busyp, *n;
 
        xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
                                        ctx->start_lsn, abort);
 
-       list_for_each_entry_safe(busyp, n, &ctx->busy_extents, list)
-               xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, busyp);
+       list_for_each_entry_safe(busyp, n, &ctx->busy_extents, list) {
+               if (!abort)
+                       xfs_discard_extent(mp, busyp);
+               xfs_alloc_busy_clear(mp, busyp);
+       }
 
        spin_lock(&ctx->cil->xc_cil_lock);
        list_del(&ctx->committing);
Index: xfs/fs/xfs/linux-2.6/xfs_discard.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_discard.c     2011-03-21 14:47:03.614474345 
+0100
+++ xfs/fs/xfs/linux-2.6/xfs_discard.c  2011-03-21 14:51:41.449976366 +0100
@@ -191,3 +191,38 @@ xfs_ioc_trim(
                return -XFS_ERROR(EFAULT);
        return 0;
 }
+
+int
+xfs_discard_extent(
+       struct xfs_mount        *mp,
+       struct xfs_busy_extent  *busyp)
+{
+       struct xfs_perag        *pag;
+       int                     error = 0;
+       xfs_daddr_t             bno;
+       int64_t                 len;
+       bool                    done  = false;
+
+       if ((mp->m_flags & XFS_MOUNT_DISCARD) == 0)
+               return 0;
+
+       bno = XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno);
+       len = XFS_FSB_TO_BB(mp, busyp->length);
+
+       pag = xfs_perag_get(mp, busyp->agno);
+       spin_lock(&pag->pagb_lock);
+       if (!busyp->length)
+               done = true;
+       busyp->flags = XFS_ALLOC_BUSY_DISCARDED;
+       spin_unlock(&pag->pagb_lock);
+       xfs_perag_put(pag);
+
+       if (done)
+               return 0;
+
+       error = -blkdev_issue_discard(mp->m_ddev_targp->bt_bdev, bno, len,
+                                     GFP_NOFS, 0);
+       if (error && error != EOPNOTSUPP)
+               xfs_info(mp, "discard failed, error %d", error);
+       return error;
+}
Index: xfs/fs/xfs/linux-2.6/xfs_discard.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_discard.h     2011-03-21 14:47:03.622475346 
+0100
+++ xfs/fs/xfs/linux-2.6/xfs_discard.h  2011-03-21 14:51:41.453973708 +0100
@@ -2,7 +2,11 @@
 #define XFS_DISCARD_H 1
 
 struct fstrim_range;
+struct xfs_busy_extent;
 
 extern int     xfs_ioc_trim(struct xfs_mount *, struct fstrim_range __user *);
 
+extern int     xfs_discard_extent(struct xfs_mount *,
+                                  struct xfs_busy_extent *);
+
 #endif /* XFS_DISCARD_H */
Index: xfs/fs/xfs/xfs_ag.h
===================================================================
--- xfs.orig/fs/xfs/xfs_ag.h    2011-03-21 14:49:21.941981228 +0100
+++ xfs/fs/xfs/xfs_ag.h 2011-03-21 14:51:41.457976522 +0100
@@ -189,6 +189,7 @@ struct xfs_busy_extent {
        xfs_extlen_t    length;
        unsigned int    flags;
 #define XFS_ALLOC_BUSY_USERDATA                0x01    /* freed data extents */
+#define XFS_ALLOC_BUSY_DISCARDED       0x02    /* can't be reused */
 };
 
 /*
Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c 2011-03-21 14:51:31.746155282 +0100
+++ xfs/fs/xfs/xfs_alloc.c      2011-03-21 14:51:41.457976522 +0100
@@ -2586,6 +2586,9 @@ xfs_alloc_busy_try_reuse(
        xfs_agblock_t   bbno = busyp->bno;
        xfs_agblock_t   bend = bbno + busyp->length;
 
+       if (busyp->flags & XFS_ALLOC_BUSY_DISCARDED)
+               return -1;
+
        if (bbno < fbno && bend > fend) {
                /*
                 * Case 1:
@@ -2778,8 +2781,9 @@ restart:
                        continue;
                }
 
-               if (!args->userdata ||
-                   (busyp->flags & XFS_ALLOC_BUSY_USERDATA)) {
+               if (!(busyp->flags & XFS_ALLOC_BUSY_DISCARDED) &&
+                   (!args->userdata ||
+                    (busyp->flags & XFS_ALLOC_BUSY_USERDATA))) {
                        int overlap;
 
                        overlap = xfs_alloc_busy_try_reuse(args->pag, busyp,

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