Re: [Cluster-devel] [PATCH v3 08/20] gfs2: Get rid of on-stack transactions

Thu, 28 Jan 2021 01:21:50 -0800 

Hi,

On 27/01/2021 21:07, Andreas Gruenbacher wrote:

On-stack transactions were introduced to work around a transaction glock
deadlock in gfs2_trans_begin in commit d8348de06f70 ("GFS2: Fix deadlock
on journal flush").  Subsequently, transaction glocks were eliminated in
favor of the more efficient freeze glocks in commit 24972557b12c ("GFS2:
remove transaction glock") without also removing the on-stack
transactions.

It has now turned out that committing on-stack transactions
significantly complicates journal free space accounting when no system
transaction (sdp->sd_log_tr) is active at the time.  It doesn't seem
that on-stack transactions provide a significant benefit beyond their
original purpose (as an optimization), so remove them to allow fixing
the journal free space accounting in a reasonable way in a subsequent
patch.

FIXME: Can we better handle a gfs2_trans_begin failure in gfs2_ail_empty_gl?
If we skip the __gfs2_ail_flush, we'll just end up with leftover items on
gl_ail_list.
The reason for the on-stack allocation is to avoid the GFP_NOFAIL allocation here. Please don't add it back, we have gradually been working to eliminate those. Thoes allocations may not fail, but they might also take a long enough time that it would make little difference if they did. So perhaps we need to look at another solution? 

Steve.




Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
---
  fs/gfs2/glops.c  | 29 +++++++----------------------
  fs/gfs2/incore.h |  1 -
  fs/gfs2/log.c    |  1 -
  fs/gfs2/trans.c  | 25 +++++++++++++------------
  fs/gfs2/trans.h  |  2 ++
  5 files changed, 22 insertions(+), 36 deletions(-)

diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 3faa421568b0..853e590ccc15 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -84,18 +84,11 @@ static void __gfs2_ail_flush(struct gfs2_glock *gl, bool 
fsync,
static int gfs2_ail_empty_gl(struct gfs2_glock *gl) 
  {
+       unsigned int revokes = atomic_read(&gl->gl_ail_count);
        struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-       struct gfs2_trans tr;
        int ret;
- memset(&tr, 0, sizeof(tr)); 
-       INIT_LIST_HEAD(&tr.tr_buf);
-       INIT_LIST_HEAD(&tr.tr_databuf);
-       INIT_LIST_HEAD(&tr.tr_ail1_list);
-       INIT_LIST_HEAD(&tr.tr_ail2_list);
-       tr.tr_revokes = atomic_read(&gl->gl_ail_count);
-
-       if (!tr.tr_revokes) {
+       if (!revokes) {
                bool have_revokes;
                bool log_in_flight;
@@ -122,20 +115,12 @@ static int gfs2_ail_empty_gl(struct gfs2_glock *gl) 
                return 0;
        }
- /* A shortened, inline version of gfs2_trans_begin() 
-         * tr->alloced is not set since the transaction structure is
-         * on the stack */
-       tr.tr_reserved = 1 + gfs2_struct2blk(sdp, tr.tr_revokes);
-       tr.tr_ip = _RET_IP_;
-       ret = gfs2_log_reserve(sdp, tr.tr_reserved);
-       if (ret < 0)
-               return ret;
-       WARN_ON_ONCE(current->journal_info);
-       current->journal_info = &tr;
-
-       __gfs2_ail_flush(gl, 0, tr.tr_revokes);
-
+       ret = __gfs2_trans_begin(sdp, 0, revokes, GFP_NOFS | __GFP_NOFAIL);
+       if (ret)
+               goto flush;
+       __gfs2_ail_flush(gl, 0, revokes);
        gfs2_trans_end(sdp);
+
  flush:
        gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
                       GFS2_LFC_AIL_EMPTY_GL);
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 8e1ab8ed4abc..958810e533ad 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -490,7 +490,6 @@ struct gfs2_quota_data {
  enum {
        TR_TOUCHED = 1,
        TR_ATTACHED = 2,
-       TR_ALLOCED = 3,
  };
struct gfs2_trans { 
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index e4dc23a24569..721d2d7f0efd 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -1114,7 +1114,6 @@ static void log_refund(struct gfs2_sbd *sdp, struct 
gfs2_trans *tr)
        if (sdp->sd_log_tr) {
                gfs2_merge_trans(sdp, tr);
        } else if (tr->tr_num_buf_new || tr->tr_num_databuf_new) {
-               gfs2_assert_withdraw(sdp, test_bit(TR_ALLOCED, &tr->tr_flags));
                sdp->sd_log_tr = tr;
                set_bit(TR_ATTACHED, &tr->tr_flags);
        }
diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
index 7705f04621f4..4f461ab37ced 100644
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -37,8 +37,8 @@ static void gfs2_print_trans(struct gfs2_sbd *sdp, const 
struct gfs2_trans *tr)
                tr->tr_num_revoke, tr->tr_num_revoke_rm);
  }
-int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks, 
-                    unsigned int revokes)
+int __gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks,
+                      unsigned int revokes, gfp_t gfp_mask)
  {
        struct gfs2_trans *tr;
        int error;
@@ -52,7 +52,7 @@ int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int 
blocks,
        if (!test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags))
                return -EROFS;
- tr = kmem_cache_zalloc(gfs2_trans_cachep, GFP_NOFS); 
+       tr = kmem_cache_zalloc(gfs2_trans_cachep, gfp_mask);
        if (!tr)
                return -ENOMEM;
@@ -60,7 +60,6 @@ int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks, 
        tr->tr_blocks = blocks;
        tr->tr_revokes = revokes;
        tr->tr_reserved = 1;
-       set_bit(TR_ALLOCED, &tr->tr_flags);
        if (blocks)
                tr->tr_reserved += 6 + blocks;
        if (revokes)
@@ -88,20 +87,23 @@ int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int 
blocks,
        return error;
  }
+int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks, 
+                    unsigned int revokes)
+{
+       return __gfs2_trans_begin(sdp, blocks, revokes, GFP_NOFS);
+}
+
  void gfs2_trans_end(struct gfs2_sbd *sdp)
  {
        struct gfs2_trans *tr = current->journal_info;
        s64 nbuf;
-       int alloced = test_bit(TR_ALLOCED, &tr->tr_flags);
current->journal_info = NULL; if (!test_bit(TR_TOUCHED, &tr->tr_flags)) { 
                gfs2_log_release(sdp, tr->tr_reserved);
-               if (alloced) {
-                       gfs2_trans_free(sdp, tr);
-                       sb_end_intwrite(sdp->sd_vfs);
-               }
+               gfs2_trans_free(sdp, tr);
+               sb_end_intwrite(sdp->sd_vfs);
                return;
        }
@@ -114,15 +116,14 @@ void gfs2_trans_end(struct gfs2_sbd *sdp) 
                gfs2_print_trans(sdp, tr);
gfs2_log_commit(sdp, tr); 
-       if (alloced && !test_bit(TR_ATTACHED, &tr->tr_flags))
+       if (!test_bit(TR_ATTACHED, &tr->tr_flags))
                gfs2_trans_free(sdp, tr);
        up_read(&sdp->sd_log_flush_lock);
if (sdp->sd_vfs->s_flags & SB_SYNCHRONOUS) 
                gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
                               GFS2_LFC_TRANS_END);
-       if (alloced)
-               sb_end_intwrite(sdp->sd_vfs);
+       sb_end_intwrite(sdp->sd_vfs);
  }
static struct gfs2_bufdata *gfs2_alloc_bufdata(struct gfs2_glock *gl, 
diff --git a/fs/gfs2/trans.h b/fs/gfs2/trans.h
index 83199ce5a5c5..9c732a5f28bf 100644
--- a/fs/gfs2/trans.h
+++ b/fs/gfs2/trans.h
@@ -34,6 +34,8 @@ static inline unsigned int gfs2_rg_blocks(const struct 
gfs2_inode *ip, unsigned
        return rgd->rd_length;
  }
+extern int __gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks, 
+                             unsigned int revokes, gfp_t gfp_mask);
  extern int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks,
                            unsigned int revokes);

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