linux-kernel - Re: [PATCH 6/9] mm/compaction: rename is_via_compact_memory to compaction_with_allocation

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Date:   Sat, 19 Aug 2023 20:14:56 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Kemeng Shi <shikemeng@...weicloud.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, david@...hat.com
Subject: Re: [PATCH 6/9] mm/compaction: rename is_via_compact_memory to
 compaction_with_allocation_order



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@...weicloud.com>
>>> ---
>>>    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 */
>>