linux-kernel - Re: [PATCH] maple_tree: Do not inline write slow path

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Date:   Thu, 21 Jul 2022 19:30:13 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     David Laight <David.Laight@...LAB.COM>
CC:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH] maple_tree: Do not inline write slow path

* David Laight <David.Laight@...LAB.COM> [220721 04:26]:
> From: Liam Howlett
> > Sent: 21 July 2022 01:53
> > 
> > Having the slow path inlined causes too much stack usage.  Create new
> > function mas_wr_bnode() to write a big node into the tree
> 
> Unless you mark the function 'noinline' the compiler is
> likely to inline it anyway.
> 
> 	David

Thanks for looking at this.

On my testing, removing the inline allowed the compiler to stop
complaining about the stack frame size.  I don't mind if it is inlined,
but I don't want to force it to be inlined.  I'd like to let the
compiler decide if it does the right thing.

Thanks,
Liam

> 
> > 
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> >  lib/maple_tree.c | 22 +++++++++++++++++-----
> >  1 file changed, 17 insertions(+), 5 deletions(-)
> > 
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index 95d8659c5a99..4c383c780162 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -4297,12 +4297,27 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
> >  	return false;
> >  }
> > 
> > +/*
> > + * mas_wr_bnode() - Slow path for a modification.
> > + * @wr_mas: The write maple state
> > + *
> > + * This is where split, rebalance end up.
> > + */
> > +static void mas_wr_bnode(struct ma_wr_state *wr_mas)
> > +{
> > +	struct maple_big_node b_node;
> > +
> > +	trace_ma_write(__func__, wr_mas->mas, 0, wr_mas->entry);
> > +	memset(&b_node, 0, sizeof(struct maple_big_node));
> > +	mas_store_b_node(wr_mas, &b_node, wr_mas->offset_end);
> > +	mas_commit_b_node(wr_mas, &b_node, wr_mas->node_end);
> > +}
> > +
> >  static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
> >  {
> >  	unsigned char node_slots;
> >  	unsigned char node_size;
> >  	struct ma_state *mas = wr_mas->mas;
> > -	struct maple_big_node b_node;
> > 
> >  	/* Direct replacement */
> >  	if (wr_mas->r_min == mas->index && wr_mas->r_max == mas->last) {
> > @@ -4338,10 +4353,7 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
> >  		return;
> > 
> >  slow_path:
> > -	memset(&b_node, 0, sizeof(struct maple_big_node));
> > -	mas_store_b_node(wr_mas, &b_node, wr_mas->offset_end);
> > -	trace_ma_write(__func__, mas, 0, wr_mas->entry);
> > -	mas_commit_b_node(wr_mas, &b_node, wr_mas->node_end);
> > +	mas_wr_bnode(wr_mas);
> >  }
> > 
> >  /*
> > --
> > 2.35.1
> 
> -
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