Re: [PATCH 2/3] maple_tree: use preallocations in mas_store_gfp()

[Sidhartha Kumar]

On 10/9/23 8:03 PM, Peng Zhang wrote:
> Hi,
>
> 在 2023/10/10 04:16, Sidhartha Kumar 写道:
> > Preallocate maple nodes before call to mas_wr_store_entry(). If a new
> > node is not needed, go directly to mas_wr_store_entry(), otherwise
> > allocate the needed nodes and set the MA_STATE_PREALLOC flag.
> >
> > Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
> > ---
> >   lib/maple_tree.c | 22 +++++++++++++++++++---
> >   1 file changed, 19 insertions(+), 3 deletions(-)
> >
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index e239197a57fc..25ae66e585f4 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -5478,17 +5478,33 @@ int mas_prealloc_calc(struct ma_wr_state *wr_mas)
> >   int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp)
> >   {
> >       MA_WR_STATE(wr_mas, mas, entry);
> > +    int request;
> >       mas_wr_store_setup(&wr_mas);
> > -    trace_ma_write(__func__, mas, 0, entry);
> > -retry:
> > +    wr_mas.content = mas_start(mas);
> > +
> > +    request = mas_prealloc_calc(&wr_mas);
> mas_wr_store_entry() does something similar to mas_prealloc_calc().
> Now, making it do it twice would incur additional overhead.
> We encountered this issue while optimizing preallocation, but it
> hasn't been resolved yet. Previously, this problem only occurred
> when using mas_preallocate(). Now, this change would bring this
> impact to all write operations on maple tree. What do you think
> about it?

After talking to Liam, I will have to implement the store type enum 
feature on the Maple Tree Work list so that mas_prealloc_calc() can 
start a partial walk and write that information to the enum. 
mas_wr_store_entry() can then read that enum to continue the walk that 
was already started rather than having to redo the whole walk. This 
could also be used in mas_preallocate(). Do you have any suggestions for 
the implementation of this enum?

Thanks,
Sid

> Thanks,
> Peng
> > +    if (!request)
> > +        goto store_entry;
> > +
> > +    mas_node_count_gfp(mas, request, gfp);
> > +    if (unlikely(mas_is_err(mas))) {
> > +        mas_set_alloc_req(mas, 0);
> > +        mas_destroy(mas);
> > +        mas_reset(mas);
> > +        return xa_err(mas->node);
> > +    }
> > +    mas->mas_flags |= MA_STATE_PREALLOC;
> > +
> > +store_entry:
> >       mas_wr_store_entry(&wr_mas);
> >       if (unlikely(mas_nomem(mas, gfp)))
> > -        goto retry;
> > +        goto store_entry;
> >       if (unlikely(mas_is_err(mas)))
> >           return xa_err(mas->node);
> > +    trace_ma_write(__func__, mas, 0, entry);
> >       return 0;
> >   }
> >   EXPORT_SYMBOL_GPL(mas_store_gfp);