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* [PATCH v7 0/2] avoid xfs transaction reservation recursion
@ 2020-08-27  1:34 Yafang Shao
  2020-08-27  1:34 ` [PATCH v7 1/2] mm: Add become_kswapd and restore_kswapd Yafang Shao
  2020-08-27  1:34 ` [PATCH v7 2/2] xfs: avoid transaction reservation recursion Yafang Shao
  0 siblings, 2 replies; 7+ messages in thread
From: Yafang Shao @ 2020-08-27  1:34 UTC (permalink / raw)
  To: david, hch, darrick.wong, willy, mhocko, akpm
  Cc: linux-xfs, linux-fsdevel, linux-mm, Yafang Shao

This patchset avoids transaction reservation recursion by reintroducing
the discarded PF_FSTRANS in a new way, suggested by Dave. In this new
implementation, four new helpers are introduced, which are
xfs_trans_context_{set, clear, update} and fstrans_context_active,
suggested by Dave. And re-using the task->journal_info to indicates
whehter the task is in fstrans or not, suggested by Willy

Patch #1 is picked from Willy's patchset "Overhaul memalloc_no*"[1]

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

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 (1):
  xfs: avoid transaction reservation recursion

 fs/iomap/buffered-io.c    |  4 ++--
 fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------
 fs/xfs/xfs_aops.c         | 11 +++++++++--
 fs/xfs/xfs_linux.h        |  4 ----
 fs/xfs/xfs_trans.c        | 19 +++++++++----------
 fs/xfs/xfs_trans.h        | 30 ++++++++++++++++++++++++++++++
 include/linux/sched/mm.h  | 23 +++++++++++++++++++++++
 include/linux/writeback.h |  3 +++
 mm/vmscan.c               | 16 +---------------
 9 files changed, 85 insertions(+), 39 deletions(-)

-- 
2.18.4


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH v7 1/2] mm: Add become_kswapd and restore_kswapd
  2020-08-27  1:34 [PATCH v7 0/2] avoid xfs transaction reservation recursion Yafang Shao
@ 2020-08-27  1:34 ` Yafang Shao
  2020-08-27  1:34 ` [PATCH v7 2/2] xfs: avoid transaction reservation recursion Yafang Shao
  1 sibling, 0 replies; 7+ messages in thread
From: Yafang Shao @ 2020-08-27  1:34 UTC (permalink / raw)
  To: david, hch, darrick.wong, willy, mhocko, akpm
  Cc: linux-xfs, linux-fsdevel, linux-mm, Yafang Shao

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Since XFS needs to pretend to be kswapd in some of its worker threads,
create methods to save & restore kswapd state.  Don't bother restoring
kswapd state in kswapd -- the only time we reach this code is when we're
exiting and the task_struct is about to be destroyed anyway.

Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------
 include/linux/sched/mm.h  | 23 +++++++++++++++++++++++
 mm/vmscan.c               | 16 +---------------
 3 files changed, 32 insertions(+), 21 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 2d25bab68764..a04a44238aab 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -2813,8 +2813,9 @@ xfs_btree_split_worker(
 {
 	struct xfs_btree_split_args	*args = container_of(work,
 						struct xfs_btree_split_args, work);
+	bool			is_kswapd = args->kswapd;
 	unsigned long		pflags;
-	unsigned long		new_pflags = PF_MEMALLOC_NOFS;
+	int			memalloc_nofs;
 
 	/*
 	 * we are in a transaction context here, but may also be doing work
@@ -2822,16 +2823,17 @@ xfs_btree_split_worker(
 	 * temporarily to ensure that we don't block waiting for memory reclaim
 	 * in any way.
 	 */
-	if (args->kswapd)
-		new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
-
-	current_set_flags_nested(&pflags, new_pflags);
+	if (is_kswapd)
+		pflags = become_kswapd();
+	memalloc_nofs = memalloc_nofs_save();
 
 	args->result = __xfs_btree_split(args->cur, args->level, args->ptrp,
 					 args->key, args->curp, args->stat);
 	complete(args->done);
 
-	current_restore_flags_nested(&pflags, new_pflags);
+	memalloc_nofs_restore(memalloc_nofs);
+	if (is_kswapd)
+		restore_kswapd(pflags);
 }
 
 /*
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index f889e332912f..b38fdcb977a4 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -303,6 +303,29 @@ static inline void memalloc_nocma_restore(unsigned int flags)
 }
 #endif
 
+/*
+ * Tell the memory management code that this thread is working on behalf
+ * of background memory reclaim (like kswapd).  That means that it will
+ * get access to memory reserves should it need to allocate memory in
+ * order to make forward progress.  With this great power comes great
+ * responsibility to not exhaust those reserves.
+ */
+#define KSWAPD_PF_FLAGS		(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD)
+
+static inline unsigned long become_kswapd(void)
+{
+	unsigned long flags = current->flags & KSWAPD_PF_FLAGS;
+
+	current->flags |= KSWAPD_PF_FLAGS;
+
+	return flags;
+}
+
+static inline void restore_kswapd(unsigned long flags)
+{
+	current->flags &= ~(flags ^ KSWAPD_PF_FLAGS);
+}
+
 #ifdef CONFIG_MEMCG
 /**
  * memalloc_use_memcg - Starts the remote memcg charging scope.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99e1796eb833..3a2615bfde35 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3859,19 +3859,7 @@ static int kswapd(void *p)
 	if (!cpumask_empty(cpumask))
 		set_cpus_allowed_ptr(tsk, cpumask);
 
-	/*
-	 * Tell the memory management that we're a "memory allocator",
-	 * and that if we need more memory we should get access to it
-	 * regardless (see "__alloc_pages()"). "kswapd" should
-	 * never get caught in the normal page freeing logic.
-	 *
-	 * (Kswapd normally doesn't need memory anyway, but sometimes
-	 * you need a small amount of memory in order to be able to
-	 * page out something else, and this flag essentially protects
-	 * us from recursively trying to free more memory as we're
-	 * trying to free the first piece of memory in the first place).
-	 */
-	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+	become_kswapd();
 	set_freezable();
 
 	WRITE_ONCE(pgdat->kswapd_order, 0);
@@ -3921,8 +3909,6 @@ static int kswapd(void *p)
 			goto kswapd_try_sleep;
 	}
 
-	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
-
 	return 0;
 }
 
-- 
2.18.4


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH v7 2/2] xfs: avoid transaction reservation recursion
  2020-08-27  1:34 [PATCH v7 0/2] avoid xfs transaction reservation recursion Yafang Shao
  2020-08-27  1:34 ` [PATCH v7 1/2] mm: Add become_kswapd and restore_kswapd Yafang Shao
@ 2020-08-27  1:34 ` Yafang Shao
  2020-08-27  1:58   ` Matthew Wilcox
  1 sibling, 1 reply; 7+ messages in thread
From: Yafang Shao @ 2020-08-27  1:34 UTC (permalink / raw)
  To: david, hch, darrick.wong, willy, mhocko, akpm
  Cc: linux-xfs, linux-fsdevel, linux-mm, Yafang Shao

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. That change is subtle.
Let's take the exmple of the check of WARN_ON_ONCE(current->flags &
PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to
PF_MEMALLOC_NOFS is not proper.
Below comment is quoted from Dave,
> It wasn't for memory allocation recursion protection in XFS - it was for
> transaction reservation recursion protection by something trying to flush
> data pages while holding a transaction reservation. Doing
> this could deadlock the journal because the existing reservation
> could prevent the nested reservation for being able to reserve space
> in the journal and that is a self-deadlock vector.
> IOWs, this check is not protecting against memory reclaim recursion
> bugs at all (that's the previous check [1]). This check is
> protecting against the filesystem calling writepages directly from a
> context where it can self-deadlock.
> So what we are seeing here is that the PF_FSTRANS ->
> PF_MEMALLOC_NOFS abstraction lost all the actual useful information
> about what type of error this check was protecting against.

As a result, we should reintroduce PF_FSTRANS. As current->journal_info
isn't used in XFS, we can reuse it to indicate whehter the task is in
fstrans or not, Per Willy. To achieve that, four new helpers are introduce
in this patch, per Dave:
- xfs_trans_context_set()
  Used in xfs_trans_alloc()
- xfs_trans_context_clear()
  Used in xfs_trans_commit() and xfs_trans_cancel()
- xfs_trans_context_update()
  Used in xfs_trans_roll()
- xfs_trans_context_active()
  To check whehter current is in fs transcation or not

This recursion check works for XFS only currently, so a new member is
introduced in struct writeback_control.

[1]. Below check is to avoid memory reclaim recursion.
if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
        PF_MEMALLOC))
        goto redirty;

Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 fs/iomap/buffered-io.c    |  4 ++--
 fs/xfs/xfs_aops.c         | 11 +++++++++--
 fs/xfs/xfs_linux.h        |  4 ----
 fs/xfs/xfs_trans.c        | 19 +++++++++----------
 fs/xfs/xfs_trans.h        | 30 ++++++++++++++++++++++++++++++
 include/linux/writeback.h |  3 +++
 6 files changed, 53 insertions(+), 18 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288dba3f..12e0fc4cb825 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
 
 	/*
 	 * Given that we do not allow direct reclaim to call us, we should
-	 * never be called in a recursive filesystem reclaim context.
+	 * never be called while in a filesystem transaction.
 	 */
-	if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
+	if (WARN_ON_ONCE(wbc->fstrans_recursion))
 		goto redirty;
 
 	/*
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index b35611882ff9..9e2eedc9d208 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -62,7 +62,8 @@ xfs_setfilesize_trans_alloc(
 	 * We hand off the transaction to the completion thread now, so
 	 * clear the flag here.
 	 */
-	current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+	xfs_trans_context_clear(tp);
+
 	return 0;
 }
 
@@ -125,7 +126,7 @@ xfs_setfilesize_ioend(
 	 * thus we need to mark ourselves as being in a transaction manually.
 	 * Similarly for freeze protection.
 	 */
-	current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+	xfs_trans_context_set(tp);
 	__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
 
 	/* we abort the update if there was an IO error */
@@ -564,6 +565,9 @@ xfs_vm_writepage(
 {
 	struct xfs_writepage_ctx wpc = { };
 
+	if (xfs_trans_context_active())
+		wbc->fstrans_recursion = 1;
+
 	return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
 }
 
@@ -574,6 +578,9 @@ xfs_vm_writepages(
 {
 	struct xfs_writepage_ctx wpc = { };
 
+	if (xfs_trans_context_active())
+		wbc->fstrans_recursion = 1;
+
 	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
 	return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops);
 }
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index ab737fed7b12..8a4f6db77e33 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -102,10 +102,6 @@ typedef __u32			xfs_nlink_t;
 #define xfs_cowb_secs		xfs_params.cowb_timer.val
 
 #define current_cpu()		(raw_smp_processor_id())
-#define current_set_flags_nested(sp, f)		\
-		(*(sp) = current->flags, current->flags |= (f))
-#define current_restore_flags_nested(sp, f)	\
-		(current->flags = ((current->flags & ~(f)) | (*(sp) & (f))))
 
 #define NBBY		8		/* number of bits per byte */
 
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index ed72867b1a19..5f3a4ff51b3c 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -153,8 +153,6 @@ xfs_trans_reserve(
 	int			error = 0;
 	bool			rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
 
-	/* Mark this thread as being in a transaction */
-	current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
 
 	/*
 	 * Attempt to reserve the needed disk blocks by decrementing
@@ -163,10 +161,8 @@ xfs_trans_reserve(
 	 */
 	if (blocks > 0) {
 		error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
-		if (error != 0) {
-			current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+		if (error != 0)
 			return -ENOSPC;
-		}
 		tp->t_blk_res += blocks;
 	}
 
@@ -241,8 +237,6 @@ xfs_trans_reserve(
 		tp->t_blk_res = 0;
 	}
 
-	current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
-
 	return error;
 }
 
@@ -284,6 +278,8 @@ xfs_trans_alloc(
 	INIT_LIST_HEAD(&tp->t_dfops);
 	tp->t_firstblock = NULLFSBLOCK;
 
+	/* Mark this thread as being in a transaction */
+	xfs_trans_context_set(tp);
 	error = xfs_trans_reserve(tp, resp, blocks, rtextents);
 	if (error) {
 		xfs_trans_cancel(tp);
@@ -878,7 +874,8 @@ __xfs_trans_commit(
 
 	xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
 
-	current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+	if (!regrant)
+		xfs_trans_context_clear(tp);
 	xfs_trans_free(tp);
 
 	/*
@@ -910,7 +907,8 @@ __xfs_trans_commit(
 			xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket);
 		tp->t_ticket = NULL;
 	}
-	current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+
+	xfs_trans_context_clear(tp);
 	xfs_trans_free_items(tp, !!error);
 	xfs_trans_free(tp);
 
@@ -971,7 +969,7 @@ xfs_trans_cancel(
 	}
 
 	/* mark this thread as no longer being in a transaction */
-	current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+	xfs_trans_context_clear(tp);
 
 	xfs_trans_free_items(tp, dirty);
 	xfs_trans_free(tp);
@@ -1013,6 +1011,7 @@ xfs_trans_roll(
 	if (error)
 		return error;
 
+	xfs_trans_context_update(trans, *tpp);
 	/*
 	 * Reserve space in the log for the next transaction.
 	 * This also pushes items in the "AIL", the list of logged items,
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index b752501818d2..f84b563438f6 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -243,4 +243,34 @@ void		xfs_trans_buf_copy_type(struct xfs_buf *dst_bp,
 
 extern kmem_zone_t	*xfs_trans_zone;
 
+static inline void
+xfs_trans_context_set(struct xfs_trans *tp)
+{
+	ASSERT(!current->journal_info);
+	current->journal_info = tp;
+	tp->t_pflags = memalloc_nofs_save();
+}
+
+static inline void
+xfs_trans_context_update(struct xfs_trans *old, struct xfs_trans *new)
+{
+	ASSERT(current->journal_info == old);
+	current->journal_info = new;
+}
+
+static inline void
+xfs_trans_context_clear(struct xfs_trans *tp)
+{
+	ASSERT(current->journal_info == tp);
+	current->journal_info = NULL;
+	memalloc_nofs_restore(tp->t_pflags);
+}
+
+static inline bool
+xfs_trans_context_active(void)
+{
+	/* Use journal_info to indicate current is in a transaction */
+	return current->journal_info != NULL;
+}
+
 #endif	/* __XFS_TRANS_H__ */
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 8e5c5bb16e2d..33f6fb901a78 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -80,6 +80,9 @@ struct writeback_control {
 
 	unsigned punt_to_cgroup:1;	/* cgrp punting, see __REQ_CGROUP_PUNT */
 
+	/* To avoid filesystem transaction reservation recursion */
+	unsigned fstrans_recursion:1;
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct bdi_writeback *wb;	/* wb this writeback is issued under */
 	struct inode *inode;		/* inode being written out */
-- 
2.18.4


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH v7 2/2] xfs: avoid transaction reservation recursion
  2020-08-27  1:34 ` [PATCH v7 2/2] xfs: avoid transaction reservation recursion Yafang Shao
@ 2020-08-27  1:58   ` Matthew Wilcox
  2020-08-27  2:13     ` Yafang Shao
  0 siblings, 1 reply; 7+ messages in thread
From: Matthew Wilcox @ 2020-08-27  1:58 UTC (permalink / raw)
  To: Yafang Shao
  Cc: david, hch, darrick.wong, mhocko, akpm, linux-xfs, linux-fsdevel,
	linux-mm

On Thu, Aug 27, 2020 at 09:34:44AM +0800, Yafang Shao wrote:
> @@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  
>  	/*
>  	 * Given that we do not allow direct reclaim to call us, we should
> -	 * never be called in a recursive filesystem reclaim context.
> +	 * never be called while in a filesystem transaction.
>  	 */
> -	if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> +	if (WARN_ON_ONCE(wbc->fstrans_recursion))
>  		goto redirty;

Erm, Dave said:

> I think we should just remove
> the check completely from iomap_writepage() and move it up into
> xfs_vm_writepage() and xfs_vm_writepages().

ie everywhere you set this new bit, just check current->journal_info.

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH v7 2/2] xfs: avoid transaction reservation recursion
  2020-08-27  1:58   ` Matthew Wilcox
@ 2020-08-27  2:13     ` Yafang Shao
  2020-08-27  2:42       ` Dave Chinner
  0 siblings, 1 reply; 7+ messages in thread
From: Yafang Shao @ 2020-08-27  2:13 UTC (permalink / raw)
  To: Matthew Wilcox
  Cc: Dave Chinner, Christoph Hellwig, Darrick J. Wong, Michal Hocko,
	Andrew Morton, linux-xfs, linux-fsdevel, Linux MM

On Thu, Aug 27, 2020 at 9:58 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Aug 27, 2020 at 09:34:44AM +0800, Yafang Shao wrote:
> > @@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> >
> >       /*
> >        * Given that we do not allow direct reclaim to call us, we should
> > -      * never be called in a recursive filesystem reclaim context.
> > +      * never be called while in a filesystem transaction.
> >        */
> > -     if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> > +     if (WARN_ON_ONCE(wbc->fstrans_recursion))
> >               goto redirty;
>
> Erm, Dave said:
>
> > I think we should just remove
> > the check completely from iomap_writepage() and move it up into
> > xfs_vm_writepage() and xfs_vm_writepages().
>
> ie everywhere you set this new bit, just check current->journal_info.


I can't get you. Would you pls. be more specific ?

I move the check of current->journal into xfs_vm_writepage() and
xfs_vm_writepages(), and I think that is the easiest way to implement
it.

       /* we abort the update if there was an IO error */
@@ -564,6 +565,9 @@ xfs_vm_writepage(
 {
        struct xfs_writepage_ctx wpc = { };

+       if (xfs_trans_context_active())
+               wbc->fstrans_recursion = 1;    <<< set for XFS only.
+
        return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
 }


--
Thanks
Yafang

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH v7 2/2] xfs: avoid transaction reservation recursion
  2020-08-27  2:13     ` Yafang Shao
@ 2020-08-27  2:42       ` Dave Chinner
  2020-08-27  2:59         ` Yafang Shao
  0 siblings, 1 reply; 7+ messages in thread
From: Dave Chinner @ 2020-08-27  2:42 UTC (permalink / raw)
  To: Yafang Shao
  Cc: Matthew Wilcox, Christoph Hellwig, Darrick J. Wong, Michal Hocko,
	Andrew Morton, linux-xfs, linux-fsdevel, Linux MM

On Thu, Aug 27, 2020 at 10:13:15AM +0800, Yafang Shao wrote:
> On Thu, Aug 27, 2020 at 9:58 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Thu, Aug 27, 2020 at 09:34:44AM +0800, Yafang Shao wrote:
> > > @@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> > >
> > >       /*
> > >        * Given that we do not allow direct reclaim to call us, we should
> > > -      * never be called in a recursive filesystem reclaim context.
> > > +      * never be called while in a filesystem transaction.
> > >        */
> > > -     if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> > > +     if (WARN_ON_ONCE(wbc->fstrans_recursion))
> > >               goto redirty;
> >
> > Erm, Dave said:
> >
> > > I think we should just remove
> > > the check completely from iomap_writepage() and move it up into
> > > xfs_vm_writepage() and xfs_vm_writepages().
> >
> > ie everywhere you set this new bit, just check current->journal_info.
> 
> 
> I can't get you. Would you pls. be more specific ?
> 
> I move the check of current->journal into xfs_vm_writepage() and
> xfs_vm_writepages(), and I think that is the easiest way to implement
> it.
> 
>        /* we abort the update if there was an IO error */
> @@ -564,6 +565,9 @@ xfs_vm_writepage(
>  {
>         struct xfs_writepage_ctx wpc = { };
> 
> +       if (xfs_trans_context_active())
> +               wbc->fstrans_recursion = 1;    <<< set for XFS only.
> +
>         return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);

Get rid of wbc->fstrans_recursion. Just do

	if (WARN_ON_ONCE(current->journal_info))
		.....

right here in the XFS code.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH v7 2/2] xfs: avoid transaction reservation recursion
  2020-08-27  2:42       ` Dave Chinner
@ 2020-08-27  2:59         ` Yafang Shao
  0 siblings, 0 replies; 7+ messages in thread
From: Yafang Shao @ 2020-08-27  2:59 UTC (permalink / raw)
  To: Dave Chinner
  Cc: Matthew Wilcox, Christoph Hellwig, Darrick J. Wong, Michal Hocko,
	Andrew Morton, linux-xfs, linux-fsdevel, Linux MM

On Thu, Aug 27, 2020 at 10:42 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Thu, Aug 27, 2020 at 10:13:15AM +0800, Yafang Shao wrote:
> > On Thu, Aug 27, 2020 at 9:58 AM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Thu, Aug 27, 2020 at 09:34:44AM +0800, Yafang Shao wrote:
> > > > @@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> > > >
> > > >       /*
> > > >        * Given that we do not allow direct reclaim to call us, we should
> > > > -      * never be called in a recursive filesystem reclaim context.
> > > > +      * never be called while in a filesystem transaction.
> > > >        */
> > > > -     if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> > > > +     if (WARN_ON_ONCE(wbc->fstrans_recursion))
> > > >               goto redirty;
> > >
> > > Erm, Dave said:
> > >
> > > > I think we should just remove
> > > > the check completely from iomap_writepage() and move it up into
> > > > xfs_vm_writepage() and xfs_vm_writepages().
> > >
> > > ie everywhere you set this new bit, just check current->journal_info.
> >
> >
> > I can't get you. Would you pls. be more specific ?
> >
> > I move the check of current->journal into xfs_vm_writepage() and
> > xfs_vm_writepages(), and I think that is the easiest way to implement
> > it.
> >
> >        /* we abort the update if there was an IO error */
> > @@ -564,6 +565,9 @@ xfs_vm_writepage(
> >  {
> >         struct xfs_writepage_ctx wpc = { };
> >
> > +       if (xfs_trans_context_active())
> > +               wbc->fstrans_recursion = 1;    <<< set for XFS only.
> > +
> >         return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
>
> Get rid of wbc->fstrans_recursion. Just do
>
>         if (WARN_ON_ONCE(current->journal_info))
>                 .....
>
> right here in the XFS code.
>

Understood.
But we have to implement the 'redirty' as well in the XFS code, that
may make the implementation more complicated.


-- 
Thanks
Yafang

^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2020-08-27  2:59 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-27  1:34 [PATCH v7 0/2] avoid xfs transaction reservation recursion Yafang Shao
2020-08-27  1:34 ` [PATCH v7 1/2] mm: Add become_kswapd and restore_kswapd Yafang Shao
2020-08-27  1:34 ` [PATCH v7 2/2] xfs: avoid transaction reservation recursion Yafang Shao
2020-08-27  1:58   ` Matthew Wilcox
2020-08-27  2:13     ` Yafang Shao
2020-08-27  2:42       ` Dave Chinner
2020-08-27  2:59         ` Yafang Shao

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