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From: Matthew Wilcox <willy@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Christoph Lameter <cl@linux.com>,
	Matthew Wilcox <mawilcox@microsoft.com>
Subject: Re: [PATCH 5/8] mm: Introduce _slub_counter_t
Date: Tue, 19 Dec 2017 04:46:05 -0800	[thread overview]
Message-ID: <20171219124605.GA13680@bombadil.infradead.org> (raw)
In-Reply-To: <20171219080731.GB2787@dhcp22.suse.cz>

On Tue, Dec 19, 2017 at 09:07:31AM +0100, Michal Hocko wrote:
> On Sat 16-12-17 08:44:22, Matthew Wilcox wrote:
> > From: Matthew Wilcox <mawilcox@microsoft.com>
> > 
> > Instead of putting the ifdef in the middle of the definition of struct
> > page, pull it forward to the rest of the ifdeffery around the SLUB
> > cmpxchg_double optimisation.
> > 
> > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> 
> The definition of struct page looks better now. I think that slub.c
> needs some love as well. I haven't checked too deeply but it seems that
> it assumes counters to be unsigned long in some places. Maybe I've
> missed some ifdef-ery but using the native type would be much better

I may have missed something, but I checked its use of 'counters' while
I was working on this patch, and I didn't *see* a problem.  The only
problem I really see is that it uses a bitfield for { inuse, objects,
frozen } and if the architecture has big-endian bitfields, it's possible
that slub's counters might end up conflicting with the special values we
use for PageBuddy, PageKmemcg and PageBalloon.  I always get confused
by big endian, so I can't even figure out how likely it is ... would
'frozen' end up as bit 31?  And if so, would _mapcount have its sign
bit at bit 31, or at bit 7?

> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

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  reply	other threads:[~2017-12-19 12:46 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-16 16:44 [PATCH 0/8] Restructure struct page Matthew Wilcox
2017-12-16 16:44 ` [PATCH 1/8] mm: Align struct page more aesthetically Matthew Wilcox
2017-12-18 15:22   ` Michal Hocko
2017-12-19 14:58   ` Christopher Lameter
2017-12-16 16:44 ` [PATCH 2/8] mm: De-indent struct page Matthew Wilcox
2017-12-18 15:36   ` Michal Hocko
2017-12-18 16:19     ` Matthew Wilcox
2017-12-18 20:49       ` Michal Hocko
2017-12-18 21:44         ` Matthew Wilcox
2017-12-19 14:59           ` Christopher Lameter
2017-12-16 16:44 ` [PATCH 3/8] mm: Remove misleading alignment claims Matthew Wilcox
2017-12-19 15:01   ` Christopher Lameter
2017-12-16 16:44 ` [PATCH 4/8] mm: Improve comment on page->mapping Matthew Wilcox
2017-12-19  8:02   ` Michal Hocko
2017-12-19 15:48     ` Christopher Lameter
2017-12-16 16:44 ` [PATCH 5/8] mm: Introduce _slub_counter_t Matthew Wilcox
2017-12-19  8:07   ` Michal Hocko
2017-12-19 12:46     ` Matthew Wilcox [this message]
2017-12-19 13:01       ` Michal Hocko
2017-12-20 16:19         ` Matthew Wilcox
2017-12-21 17:03           ` Christopher Lameter
2017-12-16 16:44 ` [PATCH 6/8] mm: Store compound_dtor / compound_order as bytes Matthew Wilcox
2017-12-19  8:19   ` Michal Hocko
2017-12-19 12:49     ` Matthew Wilcox
2017-12-16 16:44 ` [PATCH 7/8] mm: Document how to use struct page Matthew Wilcox
2017-12-16 17:47   ` Randy Dunlap
2017-12-17  1:15     ` Matthew Wilcox
2017-12-19  9:59   ` Michal Hocko
2017-12-19 13:07     ` Matthew Wilcox
2017-12-19 13:43       ` Kirill A. Shutemov
2017-12-19 13:48         ` Michal Hocko
2017-12-19 15:53   ` Christopher Lameter
2017-12-19 15:56     ` Kirill A. Shutemov
2017-12-19 16:12     ` Matthew Wilcox
2017-12-16 16:44 ` [PATCH 8/8] mm: Remove reference to PG_buddy Matthew Wilcox
2017-12-19 10:02   ` Michal Hocko
2017-12-19 15:53     ` Christopher Lameter
2017-12-17 13:06 ` [PATCH 0/8] Restructure struct page Kirill A. Shutemov
2017-12-20 15:52 Matthew Wilcox
2017-12-20 15:52 ` [PATCH 5/8] mm: Introduce _slub_counter_t Matthew Wilcox

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