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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Date:   Thu, 24 Aug 2023 10:25:04 +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 7/9] mm/compaction: factor out code to test if we should
 run compaction for target order



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.

>> 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;
>>>>>         }
>>>>>           /*
>>>>
>>>>
>>
>>