Re: [PATCH mm-unstable v1 5/5] mm/swap: remove boilerplate

[Yu Zhao]

On Fri, Jul 26, 2024 at 05:56:10PM +1200, Barry Song wrote:
> On Fri, Jul 26, 2024 at 5:48 PM Barry Song <21cnbao@xxxxxxxxx> wrote:
> >
> > On Thu, Jul 11, 2024 at 2:15 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote:
> > >
> > > Remove boilerplate by using a macro to choose the corresponding lock
> > > and handler for each folio_batch in cpu_fbatches.
> > >
> > > Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> > > ---
> > >  mm/swap.c | 107 +++++++++++++++++++-----------------------------------
> > >  1 file changed, 37 insertions(+), 70 deletions(-)
> > >
> > > diff --git a/mm/swap.c b/mm/swap.c
> > > index 4a66d2f87f26..342ff4e39ba4 100644
> > > --- a/mm/swap.c
> > > +++ b/mm/swap.c
> > > @@ -220,16 +220,45 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
> > >         folios_put(fbatch);
> > >  }
> > >
> > > -static void folio_batch_add_and_move(struct folio_batch *fbatch,
> > > -               struct folio *folio, move_fn_t move_fn)
> > > +static void __folio_batch_add_and_move(struct folio_batch *fbatch,
> > > +               struct folio *folio, move_fn_t move_fn,
> > > +               bool on_lru, bool disable_irq)
> > >  {
> > > +       unsigned long flags;
> > > +
> > > +       folio_get(folio);
> > > +
> > > +       if (on_lru && !folio_test_clear_lru(folio)) {
> > > +               folio_put(folio);
> > > +               return;
> > > +       }
> > > +
> > >         if (folio_batch_add(fbatch, folio) && !folio_test_large(folio) &&
> > >             !lru_cache_disabled())
> > >                 return;
> > >
> > > +       if (disable_irq)
> > > +               local_lock_irqsave(&cpu_fbatches.lock_irq, flags);
> > > +       else
> > > +               local_lock(&cpu_fbatches.lock);
> > > +
> > >         folio_batch_move_lru(fbatch, move_fn);
> > > +
> > > +       if (disable_irq)
> > > +               local_unlock_irqrestore(&cpu_fbatches.lock_irq, flags);
> > > +       else
> > > +               local_unlock(&cpu_fbatches.lock);
> > >  }
> > >
> > > +#define folio_batch_add_and_move(folio, op, on_lru)                                            \
> > > +       __folio_batch_add_and_move(                                                             \
> > > +               this_cpu_ptr(&cpu_fbatches.op),                                                 \
> > > +               folio,                                                                          \
> > > +               op,                                                                             \
> > > +               on_lru,                                                                         \
> > > +               offsetof(struct cpu_fbatches, op) > offsetof(struct cpu_fbatches, lock_irq)     \
> > > +       )
> >
> > I am running into this BUG, is it relevant?

Sorry for the trouble.

> > / # [   64.908801] check_preemption_disabled: 1804 callbacks suppressed
> > [   64.908915] BUG: using smp_processor_id() in preemptible [00000000]
> > code: jbd2/vda-8/96
> > [   64.909912] caller is debug_smp_processor_id+0x20/0x30
> > [   64.911743] CPU: 0 UID: 0 PID: 96 Comm: jbd2/vda-8 Not tainted
> > 6.10.0-gef32eccacce2 #59
> > [   64.912373] Hardware name: linux,dummy-virt (DT)
> > [   64.912741] Call trace:
> > [   64.913048]  dump_backtrace+0x9c/0x100
> > [   64.913414]  show_stack+0x20/0x38
> > [   64.913761]  dump_stack_lvl+0xc4/0x150
> > [   64.914197]  dump_stack+0x18/0x28
> > [   64.914557]  check_preemption_disabled+0xd8/0x120
> > [   64.914944]  debug_smp_processor_id+0x20/0x30
> > [   64.915321]  folio_add_lru+0x30/0xa8
> > [   64.915680]  filemap_add_folio+0xe4/0x118
> > [   64.916082]  __filemap_get_folio+0x178/0x450
> > [   64.916455]  __getblk_slow+0xb0/0x310
> > [   64.916816]  bdev_getblk+0x94/0xc0
> > [   64.917169]  jbd2_journal_get_descriptor_buffer+0x6c/0x1b0
> > [   64.917590]  jbd2_journal_commit_transaction+0x7f0/0x1c88
> > [   64.917994]  kjournald2+0xd4/0x278
> > [   64.918344]  kthread+0x11c/0x128
> > [   64.918693]  ret_from_fork+0x10/0x20
> 
> This removes the BUG complaint, but I'm unsure if it's the correct fix:

Below is the proper fix. Will post v2.

--- a/mm/swap.c
+++ b/mm/swap.c
@@ -221,7 +221,7 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
 	folios_put(fbatch);
 }
 
-static void __folio_batch_add_and_move(struct folio_batch *fbatch,
+static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch,
 		struct folio *folio, move_fn_t move_fn,
 		bool on_lru, bool disable_irq)
 {
@@ -234,16 +234,14 @@ static void __folio_batch_add_and_move(struct folio_batch *fbatch,
 		return;
 	}
 
-	if (folio_batch_add(fbatch, folio) && !folio_test_large(folio) &&
-	    !lru_cache_disabled())
-		return;
-
 	if (disable_irq)
 		local_lock_irqsave(&cpu_fbatches.lock_irq, flags);
 	else
 		local_lock(&cpu_fbatches.lock);
 
-	folio_batch_move_lru(fbatch, move_fn);
+	if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) ||
+	    lru_cache_disabled())
+		folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn);
 
 	if (disable_irq)
 		local_unlock_irqrestore(&cpu_fbatches.lock_irq, flags);
@@ -253,7 +251,7 @@ static void __folio_batch_add_and_move(struct folio_batch *fbatch,
 
 #define folio_batch_add_and_move(folio, op, on_lru)						\
 	__folio_batch_add_and_move(								\
-		this_cpu_ptr(&cpu_fbatches.op),							\
+		&cpu_fbatches.op,								\
 		folio,										\
 		op,										\
 		on_lru,										\