Re: [PATCH 28/42] xfs: convert xfs_alloc_vextent_iterate_ags() to use perag walker

Darrick J. Wong
2023-02-01T23:15:34Z

On Thu, Jan 19, 2023 at 09:44:51AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Now that the AG iteration code in the core allocation code has been
> cleaned up, we can easily convert it to use a for_each_perag..()
> variant to use active references and skip AGs that it can't get
> active references on.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_ag.h | 22 ++++++---
> fs/xfs/libxfs/xfs_alloc.c | 98 ++++++++++++++++++---------------------
> 2 files changed, 60 insertions(+), 60 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 8f43b91d4cf3..5e18536dfdce 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -253,6 +253,7 @@ xfs_perag_next_wrap(
> struct xfs_perag *pag,
> xfs_agnumber_t *agno,
> xfs_agnumber_t stop_agno,
> + xfs_agnumber_t restart_agno,
> xfs_agnumber_t wrap_agno)
> {
> struct xfs_mount *mp = pag->pag_mount;
> @@ -260,10 +261,11 @@ xfs_perag_next_wrap(
> *agno = pag->pag_agno + 1;
> xfs_perag_rele(pag);
> while (*agno != stop_agno) {
> - if (*agno >= wrap_agno)
> - *agno = 0;
> - if (*agno == stop_agno)
> - break;
> + if (*agno >= wrap_agno) {
> + if (restart_agno >= stop_agno)
> + break;
> + *agno = restart_agno;
> + }
>
> pag = xfs_perag_grab(mp, *agno);
> if (pag)
> @@ -274,14 +276,20 @@ xfs_perag_next_wrap(
> }
>
> /*
> - * Iterate all AGs from start_agno through wrap_agno, then 0 through
> + * Iterate all AGs from start_agno through wrap_agno, then restart_agno through
> * (start_agno - 1).
> */
> -#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
> +#define for_each_perag_wrap_range(mp, start_agno, restart_agno, wrap_agno, agno, pag) \
> for ((agno) = (start_agno), (pag) = xfs_perag_grab((mp), (agno)); \
> (pag) != NULL; \
> (pag) = xfs_perag_next_wrap((pag), &(agno), (start_agno), \
> - (wrap_agno)))
> + (restart_agno), (wrap_agno)))
> +/*
> + * Iterate all AGs from start_agno through wrap_agno, then 0 through
> + * (start_agno - 1).
> + */
> +#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
> + for_each_perag_wrap_range((mp), (start_agno), 0, (wrap_agno), (agno), (pag))
>
> /*
> * Iterate all AGs from start_agno through to the end of the filesystem, then 0
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 43a054002da3..39f3e76efcab 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -3156,6 +3156,7 @@ xfs_alloc_vextent_prepare_ag(
> if (need_pag)
> args->pag = xfs_perag_get(args->mp, args->agno);
>
> + args->agbp = NULL;
> error = xfs_alloc_fix_freelist(args, 0);
> if (error) {
> trace_xfs_alloc_vextent_nofix(args);
> @@ -3255,8 +3256,8 @@ xfs_alloc_vextent_finish(
> XFS_STATS_ADD(mp, xs_allocb, args->len);
>
> out_drop_perag:
> - if (drop_perag) {
> - xfs_perag_put(args->pag);
> + if (drop_perag && args->pag) {
> + xfs_perag_rele(args->pag);
> args->pag = NULL;
> }
> return error;
> @@ -3304,6 +3305,10 @@ xfs_alloc_vextent_this_ag(
> * we attempt to allocation in as there is no locality optimisation possible for
> * those allocations.
> *
> + * On return, args->pag may be left referenced if we finish before the "all
> + * failed" return point. The allocation finish still needs the perag, and
> + * so the caller will release it once they've finished the allocation.
> + *
> * When we wrap the AG iteration at the end of the filesystem, we have to be
> * careful not to wrap into AGs below ones we already have locked in the
> * transaction if we are doing a blocking iteration. This will result in an
> @@ -3318,72 +3323,59 @@ xfs_alloc_vextent_iterate_ags(
> uint32_t flags)
> {
> struct xfs_mount *mp = args->mp;
> + xfs_agnumber_t agno;
> int error = 0;
>
> - ASSERT(start_agno >= minimum_agno);
> +restart:
> + for_each_perag_wrap_range(mp, start_agno, minimum_agno,
> + mp->m_sb.sb_agcount, agno, args->pag) {
> + args->agno = agno;
> + trace_printk("sag %u minag %u agno %u pag %u, agbno %u, agcnt %u",
> + start_agno, minimum_agno, agno, args->pag->pag_agno,
> + target_agbno, mp->m_sb.sb_agcount);

Please remove the debugging statement or (if it's useful) convert this
to a static tracepoint.

--D

>
> - /*
> - * Loop over allocation groups twice; first time with
> - * trylock set, second time without.
> - */
> - args->agno = start_agno;
> - for (;;) {
> - args->pag = xfs_perag_get(mp, args->agno);
> error = xfs_alloc_vextent_prepare_ag(args);
> if (error)
> break;
> -
> - if (args->agbp) {
> - /*
> - * Allocation is supposed to succeed now, so break out
> - * of the loop regardless of whether we succeed or not.
> - */
> - if (args->agno == start_agno && target_agbno) {
> - args->agbno = target_agbno;
> - error = xfs_alloc_ag_vextent_near(args);
> - } else {
> - args->agbno = 0;
> - error = xfs_alloc_ag_vextent_size(args);
> - }
> - break;
> + if (!args->agbp) {
> + trace_xfs_alloc_vextent_loopfailed(args);
> + continue;
> }
>
> - trace_xfs_alloc_vextent_loopfailed(args);
> -
> /*
> - * If we are try-locking, we can't deadlock on AGF locks so we
> - * can wrap all the way back to the first AG. Otherwise, wrap
> - * back to the start AG so we can't deadlock and let the end of
> - * scan handler decide what to do next.
> + * Allocation is supposed to succeed now, so break out of the
> + * loop regardless of whether we succeed or not.
> */
> - if (++(args->agno) == mp->m_sb.sb_agcount) {
> - if (flags & XFS_ALLOC_FLAG_TRYLOCK)
> - args->agno = 0;
> - else
> - args->agno = minimum_agno;
> - }
> -
> - /*
> - * Reached the starting a.g., must either be done
> - * or switch to non-trylock mode.
> - */
> - if (args->agno == start_agno) {
> - if (flags == 0) {
> - args->agbno = NULLAGBLOCK;
> - trace_xfs_alloc_vextent_allfailed(args);
> - break;
> - }
> + if (args->agno == start_agno && target_agbno) {
> args->agbno = target_agbno;
> - flags = 0;
> + error = xfs_alloc_ag_vextent_near(args);
> + } else {
> + args->agbno = 0;
> + error = xfs_alloc_ag_vextent_size(args);
> }
> - xfs_perag_put(args->pag);
> + break;
> + }
> + if (error) {
> + xfs_perag_rele(args->pag);
> args->pag = NULL;
> + return error;
> }
> + if (args->agbp)
> + return 0;
> +
> /*
> - * The perag is left referenced in args for the caller to clean
> - * up after they've finished the allocation.
> + * We didn't find an AG we can alloation from. If we were given
> + * constraining flags by the caller, drop them and retry the allocation
> + * without any constraints being set.
> */
> - return error;
> + if (flags) {
> + flags = 0;
> + goto restart;
> + }
> +
> + ASSERT(args->pag == NULL);
> + trace_xfs_alloc_vextent_allfailed(args);
> + return 0;
> }
>
> /*
> @@ -3524,7 +3516,7 @@ xfs_alloc_vextent_near_bno(
> }
>
> if (needs_perag)
> - args->pag = xfs_perag_get(mp, args->agno);
> + args->pag = xfs_perag_grab(mp, args->agno);
>
> error = xfs_alloc_vextent_prepare_ag(args);
> if (!error && args->agbp)
> --
> 2.39.0
>