Lachlan McIlroy wrote:
> Yet another bug was found in xfs_iext_irec_compact_full() and while the
> source of the bug was found it wasn't an easy task to track it down because
> the conditions are very difficult to reproduce. Code that is difficult to
> reach is difficult to test and debug.
It might be nice to give credit to those who helped find it in the commit ;)
> xfs_iext_irec_compact_full() and xfs_iext_irec_compact_pages() are almost
> identical - they both compact indirect extent lists by moving extents from
> subsequent buffers into earlier ones. xfs_iext_irec_compact_pages() only
> moves extents if all of the extents in the next buffer will fit into the
> empty space in the buffer before it. xfs_iext_irec_compact_full() will go
> a step further and move part of the next buffer if all the extents wont fit.
> It will then shift the remaining extents in the next buffer up to the start
> of the buffer. The bug here was that we did not update er_extoff and this
> caused extent list corruption.
I'd be half-tempted to commit the fix to the code before removing it,
just in case later generations ever resurrect any of this code? *shrug*
Other than that, I think this looks ok.
-Eric
> It does not appear that this extra functionality gains us much. Calling
> xfs_iext_irec_compact_pages() instead will do a good enough job at compacting
> the indirect list and will be quicker too.
>
> For the case in xfs_iext_indirect_to_direct() the total number of extents
> in the indirect list will fit into one buffer so we will never need the
> extra functionality of xfs_iext_irec_compact_full() there.
>
> Also xfs_iext_irec_compact_pages() doesn't need to do a memmove() (the
> buffers will never overlap) so we don't want the performance hit that
> can incur.
>
> --- a/fs/xfs/xfs_inode.c 2008-09-22 13:15:33.000000000 +1000
> +++ b/fs/xfs/xfs_inode.c 2008-09-22 13:24:24.000000000 +1000
> @@ -4157,7 +4157,7 @@ xfs_iext_indirect_to_direct(
> ASSERT(nextents <= XFS_LINEAR_EXTS);
> size = nextents * sizeof(xfs_bmbt_rec_t);
>
> - xfs_iext_irec_compact_full(ifp);
> + xfs_iext_irec_compact_pages(ifp);
> ASSERT(ifp->if_real_bytes == XFS_IEXT_BUFSZ);
>
> ep = ifp->if_u1.if_ext_irec->er_extbuf;
> @@ -4488,8 +4488,7 @@ xfs_iext_irec_remove(
> * compaction policy is as follows:
> *
> * Full Compaction: Extents fit into a single page (or inline buffer)
> - * Full Compaction: Extents occupy less than 10% of allocated space
> - * Partial Compaction: Extents occupy > 10% and < 50% of allocated space
> + * Partial Compaction: Extents occupy less than 50% of allocated space
> * No Compaction: Extents occupy at least 50% of allocated space
> */
> void
> @@ -4510,8 +4509,6 @@ xfs_iext_irec_compact(
> xfs_iext_direct_to_inline(ifp, nextents);
> } else if (nextents <= XFS_LINEAR_EXTS) {
> xfs_iext_indirect_to_direct(ifp);
> - } else if (nextents < (nlists * XFS_LINEAR_EXTS) >> 3) {
> - xfs_iext_irec_compact_full(ifp);
> } else if (nextents < (nlists * XFS_LINEAR_EXTS) >> 1) {
> xfs_iext_irec_compact_pages(ifp);
> }
> @@ -4535,7 +4532,7 @@ xfs_iext_irec_compact_pages(
> erp_next = erp + 1;
> if (erp_next->er_extcount <=
> (XFS_LINEAR_EXTS - erp->er_extcount)) {
> - memmove(&erp->er_extbuf[erp->er_extcount],
> + memcpy(&erp->er_extbuf[erp->er_extcount],
> erp_next->er_extbuf, erp_next->er_extcount *
> sizeof(xfs_bmbt_rec_t));
> erp->er_extcount += erp_next->er_extcount;
> @@ -4555,91 +4552,6 @@ xfs_iext_irec_compact_pages(
> }
>
> /*
> - * Fully compact the extent records managed by the indirection array.
> - */
> -void
> -xfs_iext_irec_compact_full(
> - xfs_ifork_t *ifp) /* inode fork pointer */
> -{
> - xfs_bmbt_rec_host_t *ep, *ep_next; /* extent record pointers */
> - xfs_ext_irec_t *erp, *erp_next; /* extent irec pointers */
> - int erp_idx = 0; /* extent irec index */
> - int ext_avail; /* empty entries in ex list */
> - int ext_diff; /* number of exts to add */
> - int nlists; /* number of irec's (ex lists)
> */
> -
> - ASSERT(ifp->if_flags & XFS_IFEXTIREC);
> -
> - nlists = ifp->if_real_bytes / XFS_IEXT_BUFSZ;
> - erp = ifp->if_u1.if_ext_irec;
> - ep = &erp->er_extbuf[erp->er_extcount];
> - erp_next = erp + 1;
> - ep_next = erp_next->er_extbuf;
> -
> - while (erp_idx < nlists - 1) {
> - /*
> - * Check how many extent records are available in this irec.
> - * If there is none skip the whole exercise.
> - */
> - ext_avail = XFS_LINEAR_EXTS - erp->er_extcount;
> - if (ext_avail) {
> -
> - /*
> - * Copy over as many as possible extent records into
> - * the previous page.
> - */
> - ext_diff = MIN(ext_avail, erp_next->er_extcount);
> - memcpy(ep, ep_next, ext_diff * sizeof(xfs_bmbt_rec_t));
> - erp->er_extcount += ext_diff;
> - erp_next->er_extcount -= ext_diff;
> -
> - /*
> - * If the next irec is empty now we can simply
> - * remove it.
> - */
> - if (erp_next->er_extcount == 0) {
> - /*
> - * Free page before removing extent record
> - * so er_extoffs don't get modified in
> - * xfs_iext_irec_remove.
> - */
> - kmem_free(erp_next->er_extbuf);
> - erp_next->er_extbuf = NULL;
> - xfs_iext_irec_remove(ifp, erp_idx + 1);
> - erp = &ifp->if_u1.if_ext_irec[erp_idx];
> - nlists = ifp->if_real_bytes / XFS_IEXT_BUFSZ;
> -
> - /*
> - * If the next irec is not empty move up the content
> - * that has not been copied to the previous page to
> - * the beggining of this one.
> - */
> - } else {
> - memmove(erp_next->er_extbuf, &ep_next[ext_diff],
> - erp_next->er_extcount *
> - sizeof(xfs_bmbt_rec_t));
> - ep_next = erp_next->er_extbuf;
> - memset(&ep_next[erp_next->er_extcount], 0,
> - (XFS_LINEAR_EXTS -
> - erp_next->er_extcount) *
> - sizeof(xfs_bmbt_rec_t));
> - }
> - }
> -
> - if (erp->er_extcount == XFS_LINEAR_EXTS) {
> - erp_idx++;
> - if (erp_idx < nlists)
> - erp = &ifp->if_u1.if_ext_irec[erp_idx];
> - else
> - break;
> - }
> - ep = &erp->er_extbuf[erp->er_extcount];
> - erp_next = erp + 1;
> - ep_next = erp_next->er_extbuf;
> - }
> -}
> -
> -/*
> * This is called to update the er_extoff field in the indirection
> * array when extents have been added or removed from one of the
> * extent lists. erp_idx contains the irec index to begin updating
>
>
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