Re: [RFC v5 PATCH 9/9] xfs: relog random buffers based on errortag

[Allison Collins <allison.henderson@xxxxxxxxxx>]

On 2/27/20 6:43 AM, Brian Foster wrote:
> Since there is currently no specific use case for buffer relogging,
> add some hacky and experimental code to relog random buffers when
> the associated errortag is enabled. Update the relog reservation
> calculation appropriately and use fixed termination logic to help
> ensure that the relog queue doesn't grow indefinitely.
>
> Note that this patch was useful in causing log reservation deadlocks
> on an fsstress workload if the relog mechanism code is modified to
> acquire its own log reservation rather than rely on the relog
> pre-reservation mechanism. In other words, this helps prove that the
> relog reservation management code effectively avoids log reservation
> deadlocks.

Oh i see, so the last three are sort of an internal test case.  They 
look like they are good sand box tools for testing though.  I guess they 
dont really get RVBs since they dont apply?  Otherwise looks good for 
the purpose they are meant for.  :-)

Allison

> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> ---
>   fs/xfs/libxfs/xfs_trans_resv.c |  8 +++++++-
>   fs/xfs/xfs_trans.h             |  4 +++-
>   fs/xfs/xfs_trans_ail.c         | 11 +++++++++++
>   fs/xfs/xfs_trans_buf.c         | 13 +++++++++++++
>   4 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
> index f49b20c9ca33..59a328a0dec6 100644
> --- a/fs/xfs/libxfs/xfs_trans_resv.c
> +++ b/fs/xfs/libxfs/xfs_trans_resv.c
> @@ -840,7 +840,13 @@ STATIC uint
>   xfs_calc_relog_reservation(
>   	struct xfs_mount	*mp)
>   {
> -	return xfs_calc_qm_quotaoff_reservation(mp);
> +	uint			res;
> +
> +	res = xfs_calc_qm_quotaoff_reservation(mp);
> +#ifdef DEBUG
> +	res = max(res, xfs_calc_buf_res(4, XFS_FSB_TO_B(mp, 1)));
> +#endif
> +	return res;
>   }
>   
>   void
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index 81cb42f552d9..1783441f6d03 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -61,6 +61,7 @@ struct xfs_log_item {
>   #define	XFS_LI_DIRTY	3	/* log item dirty in transaction */
>   #define	XFS_LI_RELOG	4	/* automatically relog item */
>   #define	XFS_LI_RELOGGED	5	/* item relogged (not committed) */
> +#define	XFS_LI_RELOG_RAND 6
>   
>   #define XFS_LI_FLAGS \
>   	{ (1 << XFS_LI_IN_AIL),		"IN_AIL" }, \
> @@ -68,7 +69,8 @@ struct xfs_log_item {
>   	{ (1 << XFS_LI_FAILED),		"FAILED" }, \
>   	{ (1 << XFS_LI_DIRTY),		"DIRTY" }, \
>   	{ (1 << XFS_LI_RELOG),		"RELOG" }, \
> -	{ (1 << XFS_LI_RELOGGED),	"RELOGGED" }
> +	{ (1 << XFS_LI_RELOGGED),	"RELOGGED" }, \
> +	{ (1 << XFS_LI_RELOG_RAND),	"RELOG_RAND" }
>   
>   struct xfs_item_ops {
>   	unsigned flags;
> diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> index 103ab62e61be..9b1d7c8df6d8 100644
> --- a/fs/xfs/xfs_trans_ail.c
> +++ b/fs/xfs/xfs_trans_ail.c
> @@ -188,6 +188,17 @@ xfs_ail_relog(
>   			xfs_log_ticket_put(ailp->ail_relog_tic);
>   		spin_unlock(&ailp->ail_lock);
>   
> +		/*
> +		 * Terminate random/debug relogs at a fixed, aggressive rate to
> +		 * avoid building up too much relog activity.
> +		 */
> +		if (test_bit(XFS_LI_RELOG_RAND, &lip->li_flags) &&
> +		    ((prandom_u32() & 1) ||
> +		     (mp->m_flags & XFS_MOUNT_UNMOUNTING))) {
> +			clear_bit(XFS_LI_RELOG_RAND, &lip->li_flags);
> +			xfs_trans_relog_item_cancel(lip, false);
> +		}
> +
>   		/*
>   		 * TODO: Ideally, relog transaction management would be pushed
>   		 * down into the ->iop_push() callbacks rather than playing
> diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
> index e17715ac23fc..de7b9a68fe38 100644
> --- a/fs/xfs/xfs_trans_buf.c
> +++ b/fs/xfs/xfs_trans_buf.c
> @@ -14,6 +14,8 @@
>   #include "xfs_buf_item.h"
>   #include "xfs_trans_priv.h"
>   #include "xfs_trace.h"
> +#include "xfs_error.h"
> +#include "xfs_errortag.h"
>   
>   /*
>    * Check to see if a buffer matching the given parameters is already
> @@ -527,6 +529,17 @@ xfs_trans_log_buf(
>   
>   	trace_xfs_trans_log_buf(bip);
>   	xfs_buf_item_log(bip, first, last);
> +
> +	/*
> +	 * Relog random buffers so long as the transaction is relog enabled and
> +	 * the buffer wasn't already relogged explicitly.
> +	 */
> +	if (XFS_TEST_ERROR(false, tp->t_mountp, XFS_ERRTAG_RELOG) &&
> +	    (tp->t_flags & XFS_TRANS_RELOG) &&
> +	    !test_bit(XFS_LI_RELOG, &bip->bli_item.li_flags)) {
> +		if (xfs_trans_relog_buf(tp, bp))
> +			set_bit(XFS_LI_RELOG_RAND, &bip->bli_item.li_flags);
> +	}
>   }
>   
>