Re: [RFC v5 PATCH 3/9] xfs: automatic relogging reservation management

Brian Foster
2020-03-03T15:12:24Z

On Tue, Mar 03, 2020 at 03:07:35PM +1100, Dave Chinner wrote:
> On Tue, Mar 03, 2020 at 10:25:29AM +1100, Dave Chinner wrote:
> > On Mon, Mar 02, 2020 at 01:06:50PM -0500, Brian Foster wrote:
> > OK, XLOG_TIC_INITED is redundant, and should be removed. And
> > xfs_log_done() needs to be split into two, one for releasing the
> > ticket, one for completing the xlog_write() call. Compile tested
> > only patch below for you :P
>
> And now with sample patch.
>
> -Dave.
> --
> Dave Chinner
> david@fromorbit.com
>
> xfs: kill XLOG_TIC_INITED
>
> From: Dave Chinner <dchinner@redhat.com>
>
> Delayed logging made this redundant as we never directly write
> transactions to the log anymore. Hence we no longer make multiple
> xlog_write() calls for a transaction as we format individual items
> in a transaction, and hence don't need to keep track of whether we
> should be writing a start record for every xlog_write call.
>

FWIW the commit log could use a bit more context, perhaps from your
previous description, about the original semantics of _INITED flag.
E.g., it's always been rather vague to me, probably because it seems to
be a remnant of some no longer fully in place functionality.

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log.c | 79 ++++++++++++++++++---------------------------------
> fs/xfs/xfs_log.h | 4 ---
> fs/xfs/xfs_log_cil.c | 13 +++++----
> fs/xfs/xfs_log_priv.h | 18 ++++++------
> fs/xfs/xfs_trans.c | 24 ++++++++--------
> 5 files changed, 55 insertions(+), 83 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index f6006d94a581..a45f3eefee39 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -496,8 +496,8 @@ xfs_log_reserve(
> * This routine is called when a user of a log manager ticket is done with
> * the reservation. If the ticket was ever used, then a commit record for
> * the associated transaction is written out as a log operation header with
> - * no data. The flag XLOG_TIC_INITED is set when the first write occurs with
> - * a given ticket. If the ticket was one with a permanent reservation, then
> + * no data.

^ trailing whitespace

> + * If the ticket was one with a permanent reservation, then
> * a few operations are done differently. Permanent reservation tickets by
> * default don't release the reservation. They just commit the current
> * transaction with the belief that the reservation is still needed. A flag
> @@ -506,49 +506,38 @@ xfs_log_reserve(
> * the inited state again. By doing this, a start record will be written
> * out when the next write occurs.
> */
> -xfs_lsn_t
> -xfs_log_done(
> - struct xfs_mount *mp,
> +int
> +xlog_write_done(
> + struct xlog *log,
> struct xlog_ticket *ticket,
> struct xlog_in_core **iclog,
> - bool regrant)
> + xfs_lsn_t *lsn)
> {
> - struct xlog *log = mp->m_log;
> - xfs_lsn_t lsn = 0;
> -
> - if (XLOG_FORCED_SHUTDOWN(log) ||
> - /*
> - * If nothing was ever written, don't write out commit record.
> - * If we get an error, just continue and give back the log ticket.
> - */
> - (((ticket->t_flags & XLOG_TIC_INITED) == 0) &&
> - (xlog_commit_record(log, ticket, iclog, &lsn)))) {
> - lsn = (xfs_lsn_t) -1;
> - regrant = false;
> - }
> + if (XLOG_FORCED_SHUTDOWN(log))
> + return -EIO;
>
> + return xlog_commit_record(log, ticket, iclog, lsn);
> +}
>
> +/*
> + * Release or regrant the ticket reservation now the transaction is done with
> + * it depending on caller context. Rolling transactions need the ticket
> + * regranted, otherwise we release it completely.
> + */
> +void
> +xlog_ticket_done(
> + struct xlog *log,
> + struct xlog_ticket *ticket,
> + bool regrant)
> +{
> if (!regrant) {
> trace_xfs_log_done_nonperm(log, ticket);
> -
> - /*
> - * Release ticket if not permanent reservation or a specific
> - * request has been made to release a permanent reservation.
> - */
> xlog_ungrant_log_space(log, ticket);
> } else {
> trace_xfs_log_done_perm(log, ticket);
> -
> xlog_regrant_reserve_log_space(log, ticket);
> - /* If this ticket was a permanent reservation and we aren't
> - * trying to release it, reset the inited flags; so next time
> - * we write, a start record will be written out.
> - */
> - ticket->t_flags |= XLOG_TIC_INITED;
> }
> -
> xfs_log_ticket_put(ticket);
> - return lsn;
> }

In general it would be nicer to split off as much refactoring as
possible into separate patches, even though it's not yet clear to me
what granularity is possible with this patch...

>
> static bool
> @@ -2148,8 +2137,9 @@ xlog_print_trans(
> }
>
> /*
> - * Calculate the potential space needed by the log vector. Each region gets
> - * its own xlog_op_header_t and may need to be double word aligned.
> + * Calculate the potential space needed by the log vector. We always write a
> + * start record, and each region gets its own xlog_op_header_t and may need to
> + * be double word aligned.
> */
> static int
> xlog_write_calc_vec_length(
> @@ -2157,14 +2147,10 @@ xlog_write_calc_vec_length(
> struct xfs_log_vec *log_vector)
> {
> struct xfs_log_vec *lv;
> - int headers = 0;
> + int headers = 1;
> int len = 0;
> int i;
>
> - /* acct for start rec of xact */
> - if (ticket->t_flags & XLOG_TIC_INITED)
> - headers++;
> -
> for (lv = log_vector; lv; lv = lv->lv_next) {
> /* we don't write ordered log vectors */
> if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED)
> @@ -2195,17 +2181,11 @@ xlog_write_start_rec(
> struct xlog_op_header *ophdr,
> struct xlog_ticket *ticket)
> {
> - if (!(ticket->t_flags & XLOG_TIC_INITED))
> - return 0;
> -
> ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> ophdr->oh_clientid = ticket->t_clientid;
> ophdr->oh_len = 0;
> ophdr->oh_flags = XLOG_START_TRANS;
> ophdr->oh_res2 = 0;
> -
> - ticket->t_flags &= ~XLOG_TIC_INITED;
> -
> return sizeof(struct xlog_op_header);
> }

The header comment to this function refers to the "inited" state.

Also note that there's a similar reference in
xfs_log_write_unmount_record(), but that instance sets ->t_flags to zero
so might be fine outside of the stale comment.

>
> @@ -2410,12 +2390,10 @@ xlog_write(
> len = xlog_write_calc_vec_length(ticket, log_vector);
>
> /*
> - * Region headers and bytes are already accounted for.
> - * We only need to take into account start records and
> - * split regions in this function.
> + * Region headers and bytes are already accounted for. We only need to
> + * take into account start records and split regions in this function.
> */
> - if (ticket->t_flags & XLOG_TIC_INITED)
> - ticket->t_curr_res -= sizeof(xlog_op_header_t);
> + ticket->t_curr_res -= sizeof(xlog_op_header_t);
>

So AFAICT the CIL allocates a ticket and up to this point only mucks
around with the reservation value. That means _INITED is still in place
once we get to xlog_write(). xlog_write() immediately calls
xlog_write_calc_vec_length() and makes the ->t_curr_res adjustment
before touching ->t_flags, so those bits all seems fine.

We then get into the log vector loops, where it looks like we call
xlog_write_start_rec() for each log vector region and rely on the
_INITED flag to only write a start record once per associated ticket.
Unless I'm missing something, this looks like it would change behavior
to perhaps write a start record per-region..? Note that this might not
preclude the broader change to kill off _INITED since we're using the
same ticket throughout the call, but some initial refactoring might be
required to remove this dependency first.

> /*
> * Commit record headers need to be accounted for. These
> @@ -3609,7 +3587,6 @@ xlog_ticket_alloc(
> tic->t_ocnt = cnt;
> tic->t_tid = prandom_u32();
> tic->t_clientid = client;
> - tic->t_flags = XLOG_TIC_INITED;
> if (permanent)
> tic->t_flags |= XLOG_TIC_PERM_RESERV;
>
> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
> index 84e06805160f..85f8d0966811 100644
> --- a/fs/xfs/xfs_log.h
> +++ b/fs/xfs/xfs_log.h
> @@ -105,10 +105,6 @@ struct xfs_log_item;
> struct xfs_item_ops;
> struct xfs_trans;
>
> -xfs_lsn_t xfs_log_done(struct xfs_mount *mp,
> - struct xlog_ticket *ticket,
> - struct xlog_in_core **iclog,
> - bool regrant);
> int xfs_log_force(struct xfs_mount *mp, uint flags);
> int xfs_log_force_lsn(struct xfs_mount *mp, xfs_lsn_t lsn, uint flags,
> int *log_forced);
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 48435cf2aa16..255065d276fc 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -841,10 +841,11 @@ xlog_cil_push(
> }
> spin_unlock(&cil->xc_push_lock);
>
> - /* xfs_log_done always frees the ticket on error. */
> - commit_lsn = xfs_log_done(log->l_mp, tic, &commit_iclog, false);
> - if (commit_lsn == -1)
> - goto out_abort;
> + error = xlog_write_done(log, tic, &commit_iclog, &commit_lsn);
> + if (error)
> + goto out_abort_free_ticket;
> +
> + xlog_ticket_done(log, tic, false);
>
> spin_lock(&commit_iclog->ic_callback_lock);
> if (commit_iclog->ic_state == XLOG_STATE_IOERROR) {
> @@ -876,7 +877,7 @@ xlog_cil_push(
> return 0;
>
> out_abort_free_ticket:
> - xfs_log_ticket_put(tic);
> + xlog_ticket_done(log, tic, false);
> out_abort:
> xlog_cil_committed(ctx, true);
> return -EIO;
> @@ -1017,7 +1018,7 @@ xfs_log_commit_cil(
> if (commit_lsn)
> *commit_lsn = xc_commit_lsn;
>
> - xfs_log_done(mp, tp->t_ticket, NULL, regrant);
> + xlog_ticket_done(log, tp->t_ticket, regrant);
> tp->t_ticket = NULL;
> xfs_trans_unreserve_and_mod_sb(tp);
>
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index b192c5a9f9fd..6965d164ff45 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -53,11 +53,9 @@ enum xlog_iclog_state {
> /*
> * Flags to log ticket
> */
> -#define XLOG_TIC_INITED 0x1 /* has been initialized */
> #define XLOG_TIC_PERM_RESERV 0x2 /* permanent reservation */

These values don't end up on disk, right? If not, it might be worth
resetting the _PERM_RESERV value to 1. Otherwise the rest looks like
mostly straightforward refactoring.

Brian

>
> #define XLOG_TIC_FLAGS \
> - { XLOG_TIC_INITED, "XLOG_TIC_INITED" }, \
> { XLOG_TIC_PERM_RESERV, "XLOG_TIC_PERM_RESERV" }
>
> /*
> @@ -438,14 +436,14 @@ xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
>
> void xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
> void xlog_print_trans(struct xfs_trans *);
> -int
> -xlog_write(
> - struct xlog *log,
> - struct xfs_log_vec *log_vector,
> - struct xlog_ticket *tic,
> - xfs_lsn_t *start_lsn,
> - struct xlog_in_core **commit_iclog,
> - uint flags);
> +
> +int xlog_write(struct xlog *log, struct xfs_log_vec *log_vector,
> + struct xlog_ticket *tic, xfs_lsn_t *start_lsn,
> + struct xlog_in_core **commit_iclog, uint flags);
> +int xlog_write_done(struct xlog *log, struct xlog_ticket *ticket,
> + struct xlog_in_core **iclog, xfs_lsn_t *lsn);
> +void xlog_ticket_done(struct xlog *log, struct xlog_ticket *ticket,
> + bool regrant);
>
> /*
> * When we crack an atomic LSN, we sample it first so that the value will not
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 3b208f9a865c..85ea3727878b 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -9,6 +9,7 @@
> #include "xfs_shared.h"
> #include "xfs_format.h"
> #include "xfs_log_format.h"
> +#include "xfs_log_priv.h"
> #include "xfs_trans_resv.h"
> #include "xfs_mount.h"
> #include "xfs_extent_busy.h"
> @@ -150,8 +151,9 @@ xfs_trans_reserve(
> uint blocks,
> uint rtextents)
> {
> - int error = 0;
> - bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
> + struct xfs_mount *mp = tp->t_mountp;
> + int error = 0;
> + bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
>
> /* Mark this thread as being in a transaction */
> current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> @@ -162,7 +164,7 @@ xfs_trans_reserve(
> * fail if the count would go below zero.
> */
> if (blocks > 0) {
> - error = xfs_mod_fdblocks(tp->t_mountp, -((int64_t)blocks), rsvd);
> + error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
> if (error != 0) {
> current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> return -ENOSPC;
> @@ -191,9 +193,9 @@ xfs_trans_reserve(
>
> if (tp->t_ticket != NULL) {
> ASSERT(resp->tr_logflags & XFS_TRANS_PERM_LOG_RES);
> - error = xfs_log_regrant(tp->t_mountp, tp->t_ticket);
> + error = xfs_log_regrant(mp, tp->t_ticket);
> } else {
> - error = xfs_log_reserve(tp->t_mountp,
> + error = xfs_log_reserve(mp,
> resp->tr_logres,
> resp->tr_logcount,
> &tp->t_ticket, XFS_TRANSACTION,
> @@ -213,7 +215,7 @@ xfs_trans_reserve(
> * fail if the count would go below zero.
> */
> if (rtextents > 0) {
> - error = xfs_mod_frextents(tp->t_mountp, -((int64_t)rtextents));
> + error = xfs_mod_frextents(mp, -((int64_t)rtextents));
> if (error) {
> error = -ENOSPC;
> goto undo_log;
> @@ -229,7 +231,7 @@ xfs_trans_reserve(
> */
> undo_log:
> if (resp->tr_logres > 0) {
> - xfs_log_done(tp->t_mountp, tp->t_ticket, NULL, false);
> + xlog_ticket_done(mp->m_log, tp->t_ticket, false);
> tp->t_ticket = NULL;
> tp->t_log_res = 0;
> tp->t_flags &= ~XFS_TRANS_PERM_LOG_RES;
> @@ -237,7 +239,7 @@ xfs_trans_reserve(
>
> undo_blocks:
> if (blocks > 0) {
> - xfs_mod_fdblocks(tp->t_mountp, (int64_t)blocks, rsvd);
> + xfs_mod_fdblocks(mp, (int64_t)blocks, rsvd);
> tp->t_blk_res = 0;
> }
>
> @@ -999,9 +1001,7 @@ __xfs_trans_commit(
> */
> xfs_trans_unreserve_and_mod_dquots(tp);
> if (tp->t_ticket) {
> - commit_lsn = xfs_log_done(mp, tp->t_ticket, NULL, regrant);
> - if (commit_lsn == -1 && !error)
> - error = -EIO;
> + xlog_ticket_done(mp->m_log, tp->t_ticket, regrant);
> tp->t_ticket = NULL;
> }
> current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> @@ -1060,7 +1060,7 @@ xfs_trans_cancel(
> xfs_trans_unreserve_and_mod_dquots(tp);
>
> if (tp->t_ticket) {
> - xfs_log_done(mp, tp->t_ticket, NULL, false);
> + xlog_ticket_done(mp->m_log, tp->t_ticket, false);
> tp->t_ticket = NULL;
> }
>
>