[Cluster-devel] [PATCH v3 08/20] gfs2: Get rid of on-stack transactions
Steven Whitehouse
swhiteho at redhat.com
Thu Jan 28 09:21:27 UTC 2021
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 <agruenba at 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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