Hi all, This is an experiment I've been hacking on based on some of the recent discussions around log reservation deficiences due to unpredictable AGFL fixup behavior[1] and a previous attempt to address the problem[2]. This RFC series introduces the ability to defer AGFL block frees much like the way we already defer frees of file-mapped extents. The intent is to disconnect freeing of surplus AGFL blocks from making those free AGFL slots available for an impending allocation. In turn, this creates conditions where AGFL fixups have more consistent and predictable log reservation consumption. AGFL block allocation behavior does not change since most AGFL deficiences can be satisfied by a single allocation request (whereas AGFL blocks are generally freed one at a time, requiring multiple cycles through the allocator). This series survives the overrun reproducer associated with [1], even without the transaction fixups in [3] (that also work around the overrun). It also survives an xfstests run without any obvious problems. This is RFC for a few reasons. First, this is obviously a sensitive area of code that requires thorough analysis. This also requires more thorough stress testing than it has seen so far. Finally, the behavior changes are intentionally limited to target the reproducer workload. A proper series should probably include updates to consistently defer AGFL block frees from all possible inobt contexts, for example. I'm not so sure that is necessary/appropriate for other allocator callers, however, but is worth consideration. Thoughts, reviews, flames appreciated. Brian [1] https://marc.info/?l=linux-xfs&m=151127676203410&w=2 [2] https://marc.info/?l=linux-xfs&m=151181428131889&w=2 [3] https://marc.info/?l=linux-xfs&m=151206831911206&w=2 Brian Foster (4): xfs: create agfl block free helper function xfs: defer agfl block frees when dfops is available xfs: defer agfl block frees on extent frees xfs: defer agfl frees on inobt allocs during chunk removal fs/xfs/libxfs/xfs_alloc.c | 91 ++++++++++++++++++++++++++++++++------ fs/xfs/libxfs/xfs_alloc.h | 8 +++- fs/xfs/libxfs/xfs_defer.h | 1 + fs/xfs/libxfs/xfs_ialloc.c | 16 +++---- fs/xfs/libxfs/xfs_ialloc_btree.c | 11 +++-- fs/xfs/libxfs/xfs_ialloc_btree.h | 4 +- fs/xfs/libxfs/xfs_refcount_btree.c | 2 +- fs/xfs/libxfs/xfs_rmap.c | 2 +- fs/xfs/scrub/common.c | 8 ++-- fs/xfs/xfs_extfree_item.c | 2 +- fs/xfs/xfs_fsops.c | 2 +- fs/xfs/xfs_itable.c | 4 +- fs/xfs/xfs_trace.h | 2 + fs/xfs/xfs_trans.h | 3 +- fs/xfs/xfs_trans_extfree.c | 77 ++++++++++++++++++++++++++++++-- 15 files changed, 189 insertions(+), 44 deletions(-) -- 2.13.6 -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
