linux-kernel - Re: [PATCH v4 04/17] maple_tree: introduce mas_wr_store

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Message-ID: <20240925225904.jryrxogfzxsbacsj@master>
Date: Wed, 25 Sep 2024 22:59:04 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Sid Kumar <sidhartha.kumar@...cle.com>
Cc: Wei Yang <richard.weiyang@...il.com>, linux-kernel@...r.kernel.org,
	maple-tree@...ts.infradead.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, liam.howlett@...cle.com,
	willy@...radead.org, surenb@...gle.com
Subject: Re: [PATCH v4 04/17] maple_tree: introduce mas_wr_store_type()

On Wed, Sep 25, 2024 at 02:36:21PM -0500, Sid Kumar wrote:
>
>On 9/25/24 2:33 PM, Sid Kumar wrote:
>> 
>> On 9/24/24 9:04 PM, Wei Yang wrote:
>> > On Wed, Aug 14, 2024 at 12:19:31PM -0400, Sidhartha Kumar wrote:
>> > 
>> > Sorry for a late reply, I just see this change.
>> > 
>> > > +
>> > > +/*
>> > > + * mas_wr_store_type() - Set the store type for a given
>> > > + * store operation.
>> > > + * @wr_mas: The maple write state
>> > > + */
>> > > +static inline void mas_wr_store_type(struct ma_wr_state *wr_mas)
>> > > +{
>> > > +    struct ma_state *mas = wr_mas->mas;
>> > > +    unsigned char new_end;
>> > > +
>> > > +    if (unlikely(mas_is_none(mas) || mas_is_ptr(mas))) {
>> > > +        mas->store_type = wr_store_root;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    if (unlikely(!mas_wr_walk(wr_mas))) {
>> > > +        mas->store_type = wr_spanning_store;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    /* At this point, we are at the leaf node that needs to be
>> > > altered. */
>> > > +    mas_wr_end_piv(wr_mas);
>> > > +    if (!wr_mas->entry)
>> > > +        mas_wr_extend_null(wr_mas);
>> > > +
>> > > +    new_end = mas_wr_new_end(wr_mas);
>> > > +    if ((wr_mas->r_min == mas->index) && (wr_mas->r_max ==
>> > > mas->last)) {
>> > > +        mas->store_type = wr_exact_fit;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    if (unlikely(!mas->index && mas->last == ULONG_MAX)) {
>> > > +        mas->store_type = wr_new_root;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    /* Potential spanning rebalance collapsing a node */
>> > > +    if (new_end < mt_min_slots[wr_mas->type]) {
>> > > +        if (!mte_is_root(mas->node)) {
>> > > +            mas->store_type = wr_rebalance;
>> > > +            return;
>> > > +        }
>> > > +        mas->store_type = wr_node_store;
>> > > +        return;
>> > > +    }
>> > After this check, we are sure new_end >= mt_min_slots[wr_mas->type].
>> > 
>> > > +
>> > > +    if (new_end >= mt_slots[wr_mas->type]) {
>> > > +        mas->store_type = wr_split_store;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    if (!mt_in_rcu(mas->tree) && (mas->offset == mas->end)) {
>> > > +        mas->store_type = wr_append;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    if ((new_end == mas->end) && (!mt_in_rcu(mas->tree) ||
>> > > +        (wr_mas->offset_end - mas->offset == 1))) {
>> > > +        mas->store_type = wr_slot_store;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    if (mte_is_root(mas->node) || (new_end >=
>> > > mt_min_slots[wr_mas->type]) ||
>> > > +        (mas->mas_flags & MA_STATE_BULK)) {
>> > The check (new_end >= mt_min_slots[wr_mas->type]) here seems always
>> > be true.
>> > 
>> > So the if here seems not necessary. Do I miss something?
>> 
>> It is true that at this point new_end >= mt_min_slots[wr_mas->type] must
>> be true but if we remove that check we won't catch this wr_node_store
>> case if !mte_is_root() and !(mas->mas_flags & MA_STATE_BULK).
>> 
>> We could change the default store type to be wr_node_store and get rid of
>> that whole if statement entirely.
>> 
>> This diff passes the tests:
>> 
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c index
>> 4f34e50c92b5..2ae0c4da9d74 100644 --- a/lib/maple_tree.c +++
>> b/lib/maple_tree.c @@ -4242,14 +4242,7 @@ static inline void
>> mas_wr_store_type(struct ma_wr_state *wr_mas) return; } - if
>> (mte_is_root(mas->node) || (new_end >= mt_min_slots[wr_mas->type]) || -
>> (mas->mas_flags & MA_STATE_BULK)) { - mas->store_type = wr_node_store; -
>> return; - } - - mas->store_type = wr_invalid; - MAS_WARN_ON(mas, 1); +
>> mas->store_type = wr_node_store; }
>> 
>> do you think this makes sense?
>> 
>Sorry this diff wasn't formatted correctly, it should look normal now:
>
>diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>index 4f34e50c92b5..2ae0c4da9d74 100644
>--- a/lib/maple_tree.c
>+++ b/lib/maple_tree.c
>@@ -4242,14 +4242,7 @@ static inline void mas_wr_store_type(struct
>ma_wr_state *wr_mas)
>                return;
>        }
>
>-       if (mte_is_root(mas->node) || (new_end >= mt_min_slots[wr_mas->type])
>||
>-               (mas->mas_flags & MA_STATE_BULK)) {
>-               mas->store_type = wr_node_store;
>-               return;
>-       }
>-
>-       mas->store_type = wr_invalid;
>-       MAS_WARN_ON(mas, 1);
>+       mas->store_type = wr_node_store;
> }
>

I am ok for this one.

>> Thanks,
>> 
>> Sid
>> 
>> > > +        mas->store_type = wr_node_store;
>> > > +        return;
>> > > +    }
>> > > +
>> > > +    mas->store_type = wr_invalid;
>> > > +    MAS_WARN_ON(mas, 1);
>> > > +}
>> > > +

-- 
Wei Yang
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