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Subject: Re: [PATCH 6/9] mm/compaction: rename is_via_compact_memory to
 compaction_with_allocation_order
To:     Baolin Wang <baolin.wang@linux.alibaba.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        mgorman@techsingularity.net, david@redhat.com
References: <20230805110711.2975149-1-shikemeng@huaweicloud.com>
 <20230805110711.2975149-7-shikemeng@huaweicloud.com>
 <111c3142-e20b-3e3c-f107-cbb64a16c2b0@linux.alibaba.com>
 <d28fc70d-ea1e-4c27-a206-6c276e6e020e@huaweicloud.com>
 <bf23350e-45cc-17ef-ac2c-9efff4a70172@linux.alibaba.com>
From:   Kemeng Shi <shikemeng@huaweicloud.com>
Message-ID: <1b4fd28b-96e6-ce58-3752-759a8539c6cc@huaweicloud.com>
Date:   Tue, 22 Aug 2023 09:51:57 +0800
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on 8/19/2023 8:14 PM, Baolin Wang wrote:
> 
> 
> 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@huaweicloud.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.
I have considered rename to is_proactive_compaction. But "proactive compaction"
in comments of compaction.c mostly implies to compaction triggerred from
/proc/sys/vm/compaction_proactiveness. So "proactive compaction" itself looks
ambiguous...
> 
>>
>> 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.
> 
Sure, no insistant on this.
Is it looks good to you just change comment of is_via_compact_memory to:
We need do compaction proactively with order == -1
order == -1 is expected for proactive compaction via:
1. via /proc/sys/vm/compact_memory
2. via /sys/devices/system/node/nodex/compact
3. /proc/sys/vm/compaction_proactiveness

>>>>    {
>>>> -    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 */
>>>
> 
>