linux-kernel - Re: [PATCH v1 1/4] mm/compaction: enable compacting >0 order folios.

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Message-ID: <3F771C36-C889-448D-89B0-2202CF5EF7E2@nvidia.com>
Date:   Mon, 13 Nov 2023 14:22:30 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "\"Huang, Ying\"" <ying.huang@...el.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        "\"Yin, Fengwei\"" <fengwei.yin@...el.com>,
        Yu Zhao <yuzhao@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
        "\"Kirill A . Shutemov\"" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Kemeng Shi <shikemeng@...weicloud.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rohan Puri <rohan.puri15@...il.com>,
        Mcgrof Chamberlain <mcgrof@...nel.org>,
        Adam Manzanares <a.manzanares@...sung.com>,
        "\"Vishal Moola (Oracle)\"" <vishal.moola@...il.com>
Subject: Re: [PATCH v1 1/4] mm/compaction: enable compacting >0 order folios.

On 13 Nov 2023, at 13:30, Matthew Wilcox wrote:

> On Mon, Nov 13, 2023 at 12:01:54PM -0500, Zi Yan wrote:
>> +	/* this makes migrate_pages() split the source page and retry */
>> +	if (folio_order(src) > 0)
>> +		return NULL;
>
> Nit: folio_test_large() is more efficient than folio_order() > 0.
> The former simply tests the bit, while the second tests the bit, then
> loads folio->_order to check it's >0.  We know it will be, but there's
> no way to tell gcc that if the bit is set, this value is definitely not 0.

Got it. Make sense. Will change it in next version. Thanks.

--
Best Regards,
Yan, Zi

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