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Subject: Re: [PATCH RFC 2/4] mm/page_alloc: place pages to tail in
 __putback_isolated_page()
To:     Wei Yang <richard.weiyang@linux.alibaba.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org,
        linux-acpi@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Oscar Salvador <osalvador@suse.de>,
        Mike Rapoport <rppt@kernel.org>,
        Scott Cheloha <cheloha@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>
References: <20200916183411.64756-1-david@redhat.com>
 <20200916183411.64756-3-david@redhat.com>
 <20200918020758.GB54754@L-31X9LVDL-1304.local>
From:   David Hildenbrand <david@redhat.com>
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Message-ID: <e287e372-7b5d-9a0b-9e27-7de1e305fc3a@redhat.com>
Date:   Fri, 18 Sep 2020 09:27:23 +0200
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On 18.09.20 04:07, Wei Yang wrote:
> On Wed, Sep 16, 2020 at 08:34:09PM +0200, David Hildenbrand wrote:
>> __putback_isolated_page() already documents that pages will be placed to
>> the tail of the freelist - this is, however, not the case for
>> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
>> the case for all existing users.
>>
>> This change affects two users:
>> - free page reporting
>> - page isolation, when undoing the isolation.
>>
>> This behavior is desireable for pages that haven't really been touched
>> lately, so exactly the two users that don't actually read/write page
>> content, but rather move untouched pages.
>>
>> The new behavior is especially desirable for memory onlining, where we
>> allow allocation of newly onlined pages via undo_isolate_page_range()
>> in online_pages(). Right now, we always place them to the head of the
> 
> The code looks good, while I don't fully understand the log here.
> 
> undo_isolate_page_range() is used in __offline_pages and alloc_contig_range. I
> don't connect them with online_pages(). Do I miss something?

Yeah, please look at -mm / -next instead. See

https://lkml.kernel.org/r/20200819175957.28465-11-david@redhat.com


-- 
Thanks,

David / dhildenb