Re: [PATCH 6/9] mm/compaction: rename is_via_compact_memory to compaction_with_allocation_order

[Baolin Wang]

On 8/15/2023 8:04 PM, Kemeng Shi wrote:
> on 8/15/2023 4:58 PM, Baolin Wang wrote:
> > On 8/5/2023 7:07 PM, Kemeng Shi wrote:
> > > We have order = -1 via proactive compaction, the is_via_compact_memory is
> > > not proper name anymore.
> > > As cc->order informs the compaction to satisfy a allocation with that
> > > order, so rename it to compaction_with_allocation_order.
> > >
> > > Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> > > ---
> > >    mm/compaction.c | 11 +++++------
> > >    1 file changed, 5 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > index d8416d3dd445..b5a699ed526b 100644
> > > --- a/mm/compaction.c
> > > +++ b/mm/compaction.c
> > > @@ -2055,12 +2055,11 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
> > >    }
> > >      /*
> > > - * order == -1 is expected when compacting via
> > > - * /proc/sys/vm/compact_memory
> > > + * compact to satisfy allocation with target order
> > >     */
> > > -static inline bool is_via_compact_memory(int order)
> > > +static inline bool compaction_with_allocation_order(int order)
> >
> > I know naming is hard, but this name is not good enough that can show the compaction mode. But the original one could.
> Yes, I agree with this, but name and comment of is_via_compact_memory may
> mislead reader that order == -1 is equivalent to compaction from
> /proc/sys/vm/compact_memory.
> Actually, we have several approaches to trigger compaction with order == -1:
> 1. via /proc/sys/vm/compact_memory
> 2. via /sys/devices/system/node/nodex/compact
> 3. via proactive compact

They can all be called proactive compaction.

> Instead of indicate compaction is tirggerred by compact_memocy or anything,
> order == -1 implies if compaction is triggerrred to meet allocation with high
> order and we will stop compaction if allocation with target order will success.

IMO, the is_via_compact_memory() function helps people better 
distinguish the compaction logic we have under direct compaction or 
kcompactd compaction, while proactive compaction does not concern itself 
with these details. But compaction_with_allocation_order() will make me 
just wonder why we should compare with -1. So I don't think this patch 
is worth it, but as you said above, we can add more comments to make it 
more clear.

> > >    {
> > > -    return order == -1;
> > > +    return order != -1;
> > >    }
> > >      /*
> > > @@ -2200,7 +2199,7 @@ static enum compact_result __compact_finished(struct compact_control *cc)
> > >            goto out;
> > >        }
> > >    -    if (is_via_compact_memory(cc->order))
> > > +    if (!compaction_with_allocation_order(cc->order))
> > >            return COMPACT_CONTINUE;
> > >          /*
> > > @@ -2390,7 +2389,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> > >          cc->migratetype = gfp_migratetype(cc->gfp_mask);
> > >    -    if (!is_via_compact_memory(cc->order)) {
> > > +    if (compaction_with_allocation_order(cc->order)) {
> > >            unsigned long watermark;
> > >              /* Allocation can already succeed, nothing to do */