From: Matthew Wilcox <willy@infradead.org>
To: Christopher Lameter <cl@linux.com>
Cc: linux-mm@kvack.org, "Matthew Wilcox" <mawilcox@microsoft.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Lai Jiangshan" <jiangshanlai@gmail.com>,
"Pekka Enberg" <penberg@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Jérôme Glisse" <jglisse@redhat.com>
Subject: Re: [PATCH v4 07/16] slub: Remove page->counters
Date: Wed, 2 May 2018 10:26:39 -0700 [thread overview]
Message-ID: <20180502172639.GC2737@bombadil.infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.21.1805011148060.16325@nuc-kabylake>
On Tue, May 01, 2018 at 11:48:53AM -0500, Christopher Lameter wrote:
> On Mon, 30 Apr 2018, Matthew Wilcox wrote:
>
> > Use page->private instead, now that these two fields are in the same
> > location. Include a compile-time assert that the fields don't get out
> > of sync.
>
> Hrm. This makes the source code a bit less readable. Guess its ok.
>
> Acked-by: Christoph Lameter <cl@linux.com>
Thanks for the ACK. I'm not thrilled with this particular patch, but
I'm not thrilled with any of the other options we've come up with either.
Option 1:
Patch as written.
Pro: Keeps struct page simple
Con: Hidden dependency on page->private and page->inuse being in the same bits
Option 2:
@@ -113,9 +113,14 @@ struct page {
struct kmem_cache *slub_cache; /* shared with slab */
/* Double-word boundary */
void *slub_freelist; /* shared with slab */
- unsigned inuse:16;
- unsigned objects:15;
- unsigned frozen:1;
+ union {
+ unsigned long counters;
+ struct {
+ unsigned inuse:16;
+ unsigned objects:15;
+ unsigned frozen:1;
+ };
+ };
};
struct { /* Tail pages of compound page */
unsigned long compound_head; /* Bit zero is set */
Pro: Expresses exactly what we do.
Con: Back to five levels of indentation in struct page
Option 3: Use -fms-extensions to create a slub_page structure.
Pro: Indentation reduced to minimum and no cross-union dependencies
Con: Nobody seemed interested in the idea
Option 4: Use explicit shifting-and-masking to combine the three counters
into one word.
Con: Lots of churn.
next prev parent reply other threads:[~2018-05-02 17:26 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-30 20:22 [PATCH v4 00/16] Rearrange struct page Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 01/16] s390: Use _refcount for pgtables Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 02/16] mm: Split page_type out from _mapcount Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 03/16] mm: Mark pages in use for page tables Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 04/16] mm: Switch s_mem and slab_cache in struct page Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 05/16] mm: Move 'private' union within " Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 06/16] mm: Move _refcount out of struct page union Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 07/16] slub: Remove page->counters Matthew Wilcox
2018-05-01 16:48 ` Christopher Lameter
2018-05-02 17:26 ` Matthew Wilcox [this message]
2018-05-02 22:17 ` Kirill A. Shutemov
2018-05-03 0:52 ` Matthew Wilcox
2018-05-03 15:03 ` Christopher Lameter
2018-05-03 18:28 ` Matthew Wilcox
2018-05-04 14:55 ` Christopher Lameter
2018-05-04 15:15 ` Matthew Wilcox
2018-05-04 16:29 ` Christopher Lameter
2018-04-30 20:22 ` [PATCH v4 08/16] mm: Combine first three unions in struct page Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 09/16] mm: Use page->deferred_list Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 10/16] mm: Move lru union within struct page Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 11/16] mm: Combine first two unions in " Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 12/16] mm: Improve struct page documentation Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 13/16] mm: Add pt_mm to struct page Matthew Wilcox
2018-05-02 8:12 ` Kirill A. Shutemov
2018-05-03 0:11 ` Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 14/16] mm: Add hmm_data " Matthew Wilcox
2018-04-30 20:22 ` [PATCH v4 15/16] slab,slub: Remove rcu_head size checks Matthew Wilcox
2018-05-01 16:46 ` Christopher Lameter
2018-04-30 20:22 ` [PATCH v4 16/16] slub: Remove kmem_cache->reserved Matthew Wilcox
2018-05-01 16:43 ` Christopher Lameter
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