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Tue, 18 Apr 2023 20:01:07 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id 8ED3810C351; Wed, 19 Apr 2023 03:01:05 +0300 (+03) Date: Wed, 19 Apr 2023 03:01:05 +0300 From: "Kirill A. Shutemov" To: Johannes Weiner Cc: linux-mm@kvack.org, Kaiyang Zhao , Mel Gorman , Vlastimil Babka , David Rientjes , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [RFC PATCH 03/26] mm: make pageblock_order 2M per default Message-ID: <20230419000105.matz43p6ihrqmado@box.shutemov.name> References: <20230418191313.268131-1-hannes@cmpxchg.org> <20230418191313.268131-4-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230418191313.268131-4-hannes@cmpxchg.org> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 77228100009 X-Stat-Signature: yk7f5kx8fymjekmh4f6rtbdzcu4at7ja X-HE-Tag: 1681862469-420103 X-HE-Meta: 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 ElZFybvU jm1gIxWne9MpgTHu0fF54NXWgA2mOqQ8p0hi0SdB5D7md4oMm+zGfSGEXGlEKeyg/UpNWnWI/4Om0nXd8zUcbZCwfCzGplLjedhn8so56YBF/YexDG4U8oph/9uc8hJRvSQS7ttOSMspiEuE2QWlT701j5UIeP7RI44/v5zv3sBcg7aUaAqO3/xKYnCdv1gSTKFytFaJzh4Rjtg9+L0QC0Morm0Tc5w682YzfGsezdsVCMp2Ym/1V5rkkp20/TTRkWP7B76zHsr656wVrUdYM+ySu1ysLYH2SpAnb5chvKZyxEM8LwRua2a5H9iZZg6kIaL5VS+jHNrVd8svzTT/MWAPYggUBIMe3uRYhe0P+tPU7sdxbst3sXBQJIBZw1qaT/kUkxf2kcP6L88ZBx+rcmdw8Wv3QQtcPdALW X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 18, 2023 at 03:12:50PM -0400, Johannes Weiner wrote: > pageblock_order can be of various sizes, depending on configuration, > but the default is MAX_ORDER-1. Note that MAX_ORDER got redefined in -mm tree recently. > Given 4k pages, that comes out to > 4M. This is a large chunk for the allocator/reclaim/compaction to try > to keep grouped per migratetype. It's also unnecessary as the majority > of higher order allocations - THP and slab - are smaller than that. This seems way to x86-specific. Other arches have larger THP sizes. I believe 16M is common. Maybe define it as min(MAX_ORDER, PMD_ORDER)? > Before subsequent patches increase the effort that goes into > maintaining migratetype isolation, it's important to first set the > defrag block size to what's likely to have common consumers. > > Signed-off-by: Johannes Weiner > --- > include/linux/pageblock-flags.h | 4 ++-- > mm/page_alloc.c | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h > index 5f1ae07d724b..05b6811f8cee 100644 > --- a/include/linux/pageblock-flags.h > +++ b/include/linux/pageblock-flags.h > @@ -47,8 +47,8 @@ extern unsigned int pageblock_order; > > #else /* CONFIG_HUGETLB_PAGE */ > > -/* If huge pages are not used, group by MAX_ORDER_NR_PAGES */ > -#define pageblock_order (MAX_ORDER-1) > +/* Manage fragmentation at the 2M level */ > +#define pageblock_order ilog2(2U << (20 - PAGE_SHIFT)) > > #endif /* CONFIG_HUGETLB_PAGE */ > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ac03571e0532..5e04a69f6a26 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7634,7 +7634,7 @@ static inline void setup_usemap(struct zone *zone) {} > /* Initialise the number of pages represented by NR_PAGEBLOCK_BITS */ > void __init set_pageblock_order(void) > { > - unsigned int order = MAX_ORDER - 1; > + unsigned int order = ilog2(2U << (20 - PAGE_SHIFT)); > > /* Check that pageblock_nr_pages has not already been setup */ > if (pageblock_order) > -- > 2.39.2 > > -- Kiryl Shutsemau / Kirill A. Shutemov