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

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Date:   Thu, 24 Aug 2023 10:20:03 +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 8/22/2023 9:51 AM, Kemeng Shi wrote:
> 
> 
> 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@...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.
> 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

Look good to me. Thanks.

> 
>>>>>     {
>>>>> -    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 */
>>>>
>>
>>