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: <3aefc27b-f7b8-6832-964d-77a55ea304fc@linux.alibaba.com>
Date:   Sat, 19 Aug 2023 20:27:54 +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 8/15/2023 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?

And I think patch 8 and patch 9 should be squashed into patch 7 to 
convert all at once.

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