Re: [PATCH 5/6] [XFS] Replace per-ag array with a radix tree

Christoph Hellwig
2009-12-10T23:45:13Z

On Wed, Dec 02, 2009 at 05:11:38PM +1100, Dave Chinner wrote:
> - down_read(&mp->m_peraglock);
> + pag = xfs_perag_get(mp, ag);
> while (blen < ap->alen) {
> - pag = xfs_perag_get(mp, ag);
> if (!pag->pagf_init &&
> (error = xfs_alloc_pagf_init(mp, args.tp,
> ag, XFS_ALLOC_FLAG_TRYLOCK))) {
> xfs_perag_put(pag);
> - up_read(&mp->m_peraglock);
> return error;
> }
> /*
> @@ -2801,7 +2799,6 @@ xfs_bmap_btalloc(
> } else
> notinit = 1;
>
> - xfs_perag_put(pag);

There's a lot of those xfs_perag_get/put moved around here. Having
those merged into the patch that adds them would be a lot cleaner.

> + /* allocate the new per-ag structures */
> if (nagcount > oagcount) {
> + /* XXX: (dgc) We don't need the filestream flush anymore? */
> xfs_filestream_flush(mp);

What was the reason to have it in the first time?

> index 3727104..d6de63d 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -207,13 +207,17 @@ STATIC void
> xfs_free_perag(
> xfs_mount_t *mp)
> {
> + xfs_agnumber_t agno;
> + struct xfs_perag *pag;
> +
> + for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
> + spin_lock(&mp->m_perag_lock);
> + pag = radix_tree_delete(&mp->m_perag_tree, agno);
> + spin_unlock(&mp->m_perag_lock);
> + if (!pag)
> + continue;

Shouldn't this be a BUG_ON/ASSERT?

> + /*
> + * Walk the current per-ag tree so we don't try to initialise AGs
> + * that already exist (growfs case). Allocate and insert all the
> + * AGs we don't find ready for initialisation.
> + */
> + for (index = 0; index < agcount; index++) {
> + pag = xfs_perag_get(mp, index);
> + if (pag) {
> + xfs_perag_put(pag);
> + continue;
> + }
> + pag = kmem_zalloc(sizeof(*pag), KM_MAYFAIL);
> + if (!pag)
> + return -ENOMEM;
> + if (radix_tree_preload(GFP_NOFS))
> + return -ENOMEM;

Leaks the pag object on failure.

> mp->m_maxagi = xfs_initialize_perag(mp, sbp->sb_agcount);
> + if ((int)mp->m_maxagi < 0) {
> + cmn_err(CE_WARN, "XFS: Failed per-ag initialisation: %d",
> + (int)mp->m_maxagi);
> + error = mp->m_maxagi;
>
Just assign it to error first and then later to mp->m_maxagi to avoid
the cast?

> static inline xfs_perag_t *
> xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
> {
> - return &mp->m_perag[agno];
> + struct xfs_perag *pag;
> +
> + spin_lock(&mp->m_perag_lock);
> + pag = radix_tree_lookup(&mp->m_perag_tree, agno);
> + spin_unlock(&mp->m_perag_lock);
> + return pag;

Can't we do this as a lock-less (at least for lookups) radix tree?

And btw, I think we should still have a global sleeping lock to
serialize the whole growfs operation against other potentional growfs
callers.