linux-kernel - Re: [PATCH 7/9] mm/compaction: factor out code to test if we should run compaction for target order

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Message-ID: <0e907eb6-db69-503c-1d17-a26fc53c8384@huaweicloud.com>
Date:   Thu, 24 Aug 2023 10:59:39 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, david@...hat.com
Subject: Re: [PATCH 7/9] mm/compaction: factor out code to test if we should
 run compaction for target order



on 8/24/2023 10:25 AM, Baolin Wang wrote:
> 
> 
> On 8/22/2023 9:57 AM, Kemeng Shi wrote:
>>
>>
>> on 8/19/2023 8:27 PM, Baolin Wang wrote:
>>>
>>>
>>> On 8/15/2023 8:10 PM, Kemeng Shi wrote:
>>>>
>>>>
>>>> on 8/15/2023 4:53 PM, Baolin Wang wrote:
>>>>>
>>>>>
>>>>> On 8/5/2023 7:07 PM, Kemeng Shi wrote:
>>>>>> We always do zone_watermark_ok check and compaction_suitable check
>>>>>> together to test if compaction for target order should be runned.
>>>>>> Factor these code out for preparation to remove repeat code.
>>>>>>
>>>>>> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
>>>>>> ---
>>>>>>     mm/compaction.c | 42 +++++++++++++++++++++++++++++-------------
>>>>>>     1 file changed, 29 insertions(+), 13 deletions(-)
>>>>>>
>>>>>> diff --git a/mm/compaction.c b/mm/compaction.c
>>>>>> index b5a699ed526b..26787ebb0297 100644
>>>>>> --- a/mm/compaction.c
>>>>>> +++ b/mm/compaction.c
>>>>>> @@ -2365,6 +2365,30 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
>>>>>>         return false;
>>>>>>     }
>>>>>>     +/*
>>>>>> + * Should we do compaction for target allocation order.
>>>>>> + * Return COMPACT_SUCCESS if allocation for target order can be already
>>>>>> + * satisfied
>>>>>> + * Return COMPACT_SKIPPED if compaction for target order is likely to fail
>>>>>> + * Return COMPACT_CONTINUE if compaction for target order should be runned
>>>>>> + */
>>>>>> +static inline enum compact_result
>>>>>> +compaction_suit_allocation_order(struct zone *zone, unsigned int order,
>>>>>> +                 int highest_zoneidx, unsigned int alloc_flags)
>>>>>> +{
>>>>>> +    unsigned long watermark;
>>>>>> +
>>>>>> +    watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
>>>>>
>>>>> IIUC, the watermark used in patch 8 and patch 9 is different, right? Have you measured the impact of modifying this watermark?
>>>>>
>>>> Actually, there is no functional change intended. Consider wmark_pages with
>>>> alloc_flags = 0 is equivalent to min_wmark_pages, patch 8 and patch 9 still
>>>> use original watermark.
>>>
>>> Can you use ALLOC_WMARK_MIN macro to make it more clear?
>> Sorry, I can't quite follow this. The watermark should differ with different
>> alloc_flags instead of WMARK_MIN hard-coded.
>> Patch 8 and patch 9 use watermark with WMARK_MIN as they get alloc_flags = 0.
> 
> I mean you can pass 'alloc_flags=ALLOC_WMARK_MIN' instead of a magic number 0 when calling compaction_suit_allocation_order() in patch 8 and patch 9.
> 
Thanks for explain and this do make it better. I will do this in next version.
>>> And I think patch 8 and patch 9 should be squashed into patch 7 to convert all at once.
>> Sure, i could do this in next version.
>>>
>>>>>> +    if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
>>>>>> +                  alloc_flags))
>>>>>> +        return COMPACT_SUCCESS;
>>>>>> +
>>>>>> +    if (!compaction_suitable(zone, order, highest_zoneidx))
>>>>>> +        return COMPACT_SKIPPED;
>>>>>> +
>>>>>> +    return COMPACT_CONTINUE;
>>>>>> +}
>>>>>> +
>>>>>>     static enum compact_result
>>>>>>     compact_zone(struct compact_control *cc, struct capture_control *capc)
>>>>>>     {
>>>>>> @@ -2390,19 +2414,11 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>>>>>>         cc->migratetype = gfp_migratetype(cc->gfp_mask);
>>>>>>           if (compaction_with_allocation_order(cc->order)) {
>>>>>> -        unsigned long watermark;
>>>>>> -
>>>>>> -        /* Allocation can already succeed, nothing to do */
>>>>>> -        watermark = wmark_pages(cc->zone,
>>>>>> -                    cc->alloc_flags & ALLOC_WMARK_MASK);
>>>>>> -        if (zone_watermark_ok(cc->zone, cc->order, watermark,
>>>>>> -                      cc->highest_zoneidx, cc->alloc_flags))
>>>>>> -            return COMPACT_SUCCESS;
>>>>>> -
>>>>>> -        /* Compaction is likely to fail */
>>>>>> -        if (!compaction_suitable(cc->zone, cc->order,
>>>>>> -                     cc->highest_zoneidx))
>>>>>> -            return COMPACT_SKIPPED;
>>>>>> +        ret = compaction_suit_allocation_order(cc->zone, cc->order,
>>>>>> +                               cc->highest_zoneidx,
>>>>>> +                               cc->alloc_flags);
>>>>>> +        if (ret != COMPACT_CONTINUE)
>>>>>> +            return ret;
>>>>>>         }
>>>>>>           /*
>>>>>
>>>>>
>>>
>>>
>