On 2021-08-17 11:17:18 [+0200], Vlastimil Babka wrote:
> On 8/17/21 11:12 AM, Sebastian Andrzej Siewior wrote:
> > On 2021-08-17 10:37:48 [+0200], Vlastimil Babka wrote:
> >> OK reproduced. Thanks, will investigate.
> >
> > With the local_lock at the top, the needed alignment gets broken for dbl
> > cmpxchg. On RT it was working ;)
>
> I'd rather have page and partial in the same cacheline as well, is it ok
> to just move the lock as last and not care about whether it straddles
> cachelines or not? (with CONFIG_SLUB_CPU_PARTIAL it will naturally start
> with the next cacheline).
Moving like you suggested appears to be more efficient and saves a bit
of memory:
RT+ debug:
struct kmem_cache_cpu {
void * * freelist; /* 0 8 */
long unsigned int tid; /* 8 8 */
struct page * page; /* 16 8 */
struct page * partial; /* 24 8 */
local_lock_t lock; /* 32 144 */
/* size: 176, cachelines: 3, members: 5 */
/* last cacheline: 48 bytes */
};
RT no debug:
struct kmem_cache_cpu {
void * * freelist; /* 0 8 */
long unsigned int tid; /* 8 8 */
struct page * page; /* 16 8 */
struct page * partial; /* 24 8 */
local_lock_t lock; /* 32 32 */
/* size: 64, cachelines: 1, members: 5 */
};
no-RT, no-debug:
struct kmem_cache_cpu {
void * * freelist; /* 0 8 */
long unsigned int tid; /* 8 8 */
struct page * page; /* 16 8 */
struct page * partial; /* 24 8 */
local_lock_t lock; /* 32 0 */
/* size: 32, cachelines: 1, members: 5 */
/* last cacheline: 32 bytes */
};
no-RT, debug:
struct kmem_cache_cpu {
void * * freelist; /* 0 8 */
long unsigned int tid; /* 8 8 */
struct page * page; /* 16 8 */
struct page * partial; /* 24 8 */
local_lock_t lock; /* 32 56 */
/* size: 88, cachelines: 2, members: 5 */
/* last cacheline: 24 bytes */
};
Sebastian
