linux-kernel - Re: [PATCH] mm, compaction: fast_find_migrateblock() should return pfn in the target zone

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Date:   Wed, 11 May 2022 17:26:16 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Rei Yamamoto <yamamoto.rei@...fujitsu.com>
CC:     <akpm@...ux-foundation.org>, <aquini@...hat.com>,
        <ddutile@...hat.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <mgorman@...hsingularity.net>,
        <vvghjk1234@...il.com>
Subject: Re: [PATCH] mm, compaction: fast_find_migrateblock() should return
 pfn in the target zone

On 2022/5/11 15:07, Rei Yamamoto wrote:
> On Wed, 11 May 2022 14:25:34 Miaohe Lin wrote:
>> On 2022/5/11 12:43, Rei Yamamoto wrote:
>>> Prevent returning a pfn outside the target zone in case that not
>>> aligned with pageblock boundary.
>>> Otherwise isolate_migratepages_block() would handle pages not in
>>> the target zone.
>>>
>>
>> IIUC, the sole caller isolate_migratepages will ensure the pfn won't outside
>> the target zone. So the below code change might not be necessary. Or am I miss
>> something ?
> 
> While block_start_pfn is ensured, this variable is not used as the argument for 
> isolate_migratepages_block():
>   -----
>   static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   {
>   :
>           low_pfn = fast_find_migrateblock(cc);
>           block_start_pfn = pageblock_start_pfn(low_pfn);
>           if (block_start_pfn < cc->zone->zone_start_pfn)
>                   block_start_pfn = cc->zone->zone_start_pfn;  <--- block_start_pfn is ensured not outside 
>                                                                     the target zone
>   :
>           block_end_pfn = pageblock_end_pfn(low_pfn);
>   :
>           for (; block_end_pfn <= cc->free_pfn;
>                           fast_find_block = false,
>                           cc->migrate_pfn = low_pfn = block_end_pfn,
>                           block_start_pfn = block_end_pfn,
>                           block_end_pfn += pageblock_nr_pages) {
>   :
>                   if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,  <--- low_pfn is passed as 
>                                                                                    the argument

Sorry, I think you're right. And could you please add the runtime effect of this issue?

Anyway, this patch looks good to me now. Thanks!

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

>                                                   isolate_mode))
>                           return ISOLATE_ABORT;
>   -----
> 
> So, the low_pfn passed to isolate_migratepages_block() can be outside the target zone.
> 
> Thanks,
> Rei
> .
>