[PATCH v13 0/4] xfs: avoid transaction reservation recursion

[Yafang Shao <laoar.shao@gmail.com>]

PF_FSTRANS which is used to avoid transaction reservation recursion, is
dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
memalloc_nofs_{save,restore} API"), and replaced by PF_MEMALLOC_NOFS which
means to avoid filesystem reclaim recursion.

As these two flags have different meanings, we'd better reintroduce
PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct,
we can reuse the current->journal_info to do that, per Willy. As the 
check of transaction reservation recursion is used by XFS only, we can 
move the check into xfs_vm_writepage(s), per Dave.

Patch #1 and #2 are to use the memalloc_nofs_{save,restore} API 
Patch #1 is picked form Willy's patchset "Overhaul memalloc_no*"[1]

Patch #3 is the refactor of xfs_trans context, which is activated when
xfs_trans is allocated and deactivated when xfs_trans is freed.

Patch #4 is the implementation of reusing current->journal_info to
avoid transaction reservation recursion.

No obvious error occurred after running xfstests.

[1]. https://lore.kernel.org/linux-mm/20200625113122.7540-1-willy@infradead.org

v13:
- move xfs_trans_context_swap() into patch #3 and set NOFS to the old
  transaction

v12:
Per Darrick's suggestion,
- add the check before calling xfs_trans_context_clear() in
  xfs_trans_context_free().
- move t_pflags into xfs_trans_context_swap()

v11:
- add the warning at the callsite of xfs_trans_context_active()
- improve the commit log of patch #2

v10:
- refactor the code, per Dave.

v9:
- rebase it on xfs tree.
- Darrick fixed an error occurred in xfs/141
- run xfstests, and no obvious error occurred.

v8:
- check xfs_trans_context_active() in xfs_vm_writepage(s), per Dave.

v7:
- check fstrans recursion for XFS only, by introducing a new member in
  struct writeback_control.

v6:
- add Michal's ack and comment in patch #1.

v5:
- pick one of Willy's patch
- introduce four new helpers, per Dave

v4:
- retitle from "xfs: introduce task->in_fstrans for transaction reservation
  recursion protection"
- reuse current->journal_info, per Willy

Matthew Wilcox (Oracle) (1):
  mm: Add become_kswapd and restore_kswapd

Yafang Shao (3):
  xfs: use memalloc_nofs_{save,restore} in xfs transaction
  xfs: refactor the usage around xfs_trans_context_{set,clear}
  xfs: use current->journal_info to avoid transaction reservation
    recursion

 fs/iomap/buffered-io.c    |  7 -------
 fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------
 fs/xfs/xfs_aops.c         | 21 +++++++++++++++++++--
 fs/xfs/xfs_linux.h        |  4 ----
 fs/xfs/xfs_trans.c        | 26 ++++++++++++--------------
 fs/xfs/xfs_trans.h        | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/sched/mm.h  | 23 +++++++++++++++++++++++
 mm/vmscan.c               | 16 +---------------
 8 files changed, 100 insertions(+), 48 deletions(-)

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2.18.4