On Mon, Sep 09, 2019 at 11:51:59AM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > In certain situations the background CIL push can be indefinitely > delayed. While we have workarounds from the obvious cases now, it > doesn't solve the underlying issue. This issue is that there is no > upper limit on the CIL where we will either force or wait for > a background push to start, hence allowing the CIL to grow without > bound until it consumes all log space. > > To fix this, add a new wait queue to the CIL which allows background > pushes to wait for the CIL context to be switched out. This happens > when the push starts, so it will allow us to block incoming > transaction commit completion until the push has started. This will > only affect processes that are running modifications, and only when > the CIL threshold has been significantly overrun. > > This has no apparent impact on performance, and doesn't even trigger > until over 45 million inodes had been created in a 16-way fsmark > test on a 2GB log. That was limiting at 64MB of log space used, so > the active CIL size is only about 3% of the total log in that case. > The concurrent removal of those files did not trigger the background > sleep at all. > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > --- > fs/xfs/xfs_log_cil.c | 30 +++++++++++++++++++++++++----- > fs/xfs/xfs_log_priv.h | 1 + > 2 files changed, 26 insertions(+), 5 deletions(-) > > diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c > index ef652abd112c..eec9b32f5e08 100644 > --- a/fs/xfs/xfs_log_cil.c > +++ b/fs/xfs/xfs_log_cil.c > @@ -670,6 +670,11 @@ xlog_cil_push( > push_seq = cil->xc_push_seq; > ASSERT(push_seq <= ctx->sequence); > > + /* > + * Wake up any background push waiters now this context is being pushed. > + */ > + wake_up_all(&ctx->push_wait); > + > /* > * Check if we've anything to push. If there is nothing, then we don't > * move on to a new sequence number and so we have to be able to push > @@ -746,6 +751,7 @@ xlog_cil_push( > */ > INIT_LIST_HEAD(&new_ctx->committing); > INIT_LIST_HEAD(&new_ctx->busy_extents); > + init_waitqueue_head(&new_ctx->push_wait); > new_ctx->sequence = ctx->sequence + 1; > new_ctx->cil = cil; > cil->xc_ctx = new_ctx; > @@ -898,7 +904,7 @@ xlog_cil_push_work( > * checkpoint), but commit latency and memory usage limit this to a smaller > * size. > */ > -static void > +static bool > xlog_cil_push_background( > struct xlog *log) > { > @@ -915,14 +921,28 @@ xlog_cil_push_background( > * space available yet. > */ > if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log)) > - return; > + return false; > > spin_lock(&cil->xc_push_lock); > if (cil->xc_push_seq < cil->xc_current_sequence) { > cil->xc_push_seq = cil->xc_current_sequence; > queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work); > } > + > + /* > + * If we are well over the space limit, throttle the work that is being > + * done until the push work on this context has begun. This will prevent > + * the CIL from violating maximum transaction size limits if the CIL > + * push is delayed for some reason. > + */ > + if (cil->xc_ctx->space_used > XLOG_CIL_SPACE_LIMIT(log) * 2) { > + up_read(&cil->xc_ctx_lock); > + trace_printk("CIL space used %d", cil->xc_ctx->space_used); Needs a real tracepoint before this drops RFC status. > + xlog_wait(&cil->xc_ctx->push_wait, &cil->xc_push_lock); > + return true; > + } > spin_unlock(&cil->xc_push_lock); > + return false; > > } > > @@ -1038,9 +1058,8 @@ xfs_log_commit_cil( > if (lip->li_ops->iop_committing) > lip->li_ops->iop_committing(lip, xc_commit_lsn); > } > - xlog_cil_push_background(log); > - > - up_read(&cil->xc_ctx_lock); > + if (!xlog_cil_push_background(log)) > + up_read(&cil->xc_ctx_lock); Hmmmm... the return value here tell us if ctx_lock has been dropped. /me wonders if this would be cleaner if xlog_cil_push_background returned having called up_read...? --D > } > > /* > @@ -1199,6 +1218,7 @@ xlog_cil_init( > > INIT_LIST_HEAD(&ctx->committing); > INIT_LIST_HEAD(&ctx->busy_extents); > + init_waitqueue_head(&ctx->push_wait); > ctx->sequence = 1; > ctx->cil = cil; > cil->xc_ctx = ctx; > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index 187a43ffeaf7..466259fd1e4a 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -247,6 +247,7 @@ struct xfs_cil_ctx { > struct xfs_log_vec *lv_chain; /* logvecs being pushed */ > struct list_head iclog_entry; > struct list_head committing; /* ctx committing list */ > + wait_queue_head_t push_wait; /* background push throttle */ > struct work_struct discard_endio_work; > }; > > -- > 2.23.0.rc1 >