Re: [PATCH 3/3] Remove MINIMUM_OBJECT_SIZE

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 19/07/2021 11:03, Owen Smith wrote:
> MINIMUM_OBJECT_SIZE would make all cached objects at least 0x80 bytes, which
> would limit the number of objects in each slab to 31 objects.
>
> This limitation is not needed, as the slab's mask is dynamically allocated to
> cope with the correct number of objects that can fit into a single slab.
> Cache object's sizes are rounded up to the nearest pointer boundary to maintain
> object alignment. Removing the minimum size allows more objects per cache slab,
> reducing the memory overhead of caches.
Yes, that restriction dates from a time when the slab mask was inline.

> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
Acked-by: Paul Durrant <paul@xxxxxxx>

> ---
>   src/xenbus/cache.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/src/xenbus/cache.c b/src/xenbus/cache.c
> index d695ee3..a24c4e5 100644
> --- a/src/xenbus/cache.c
> +++ b/src/xenbus/cache.c
> @@ -66,12 +66,8 @@ typedef struct _XENBUS_CACHE_SLAB {
>       UCHAR           Buffer[1];
>   } XENBUS_CACHE_SLAB, *PXENBUS_CACHE_SLAB;
>   
> -#define BITS_PER_ULONG (sizeof (ULONG) * 8)
> -#define MINIMUM_OBJECT_SIZE (PAGE_SIZE / BITS_PER_ULONG)
> -
> -C_ASSERT(sizeof (XENBUS_CACHE_SLAB) <= MINIMUM_OBJECT_SIZE);
> -
> -#define MAXNAMELEN  128
> +#define BITS_PER_ULONG  (sizeof (ULONG) * 8)
> +#define MAXNAMELEN      128
>   
>   struct _XENBUS_CACHE {
>       LIST_ENTRY              ListEntry;
> @@ -806,7 +802,6 @@ CacheCreate(
>       if (!NT_SUCCESS(status))
>           goto fail2;
>   
> -    Size = __max(Size, MINIMUM_OBJECT_SIZE);
>       Size = P2ROUNDUP(Size, sizeof (ULONG_PTR));
>   
>       if (Cap == 0)