Re: [PATCH 3/7] zram: Speed insertion of new pages with cached idx

Robert Jennings
2011-01-26T19:50:57Z

* Pekka Enberg (penberg@cs.helsinki.fi) wrote:
> On Wed, Jan 26, 2011 at 7:23 PM, Robert Jennings> <rcj@linux.vnet.ibm.com> wrote:
>> Calculate the first- and second-level indices for new page when the pool
>> is initialized rather than calculating them on each insertion.
>>
>> Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
>> ---
>> drivers/staging/zram/xvmalloc.c | 13 +++++++++++--
>> drivers/staging/zram/xvmalloc_int.h | 4 ++++
>> 2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/zram/xvmalloc.c b/drivers/staging/zram/xvmalloc.c
>> index 3fdbb8a..a507f95 100644
>> --- a/drivers/staging/zram/xvmalloc.c
>> +++ b/drivers/staging/zram/xvmalloc.c
>> @@ -184,8 +184,13 @@ static void insert_block(struct xv_pool *pool, struct page *page, u32 offset,
>> u32 flindex, slindex;
>> struct block_header *nextblock;
>>
>> - slindex = get_index_for_insert(block->size);
>> - flindex = slindex / BITS_PER_LONG;
>> + if (block->size >= (PAGE_SIZE - XV_ALIGN)) {
>> + slindex = pagesize_slindex;
>> + flindex = pagesize_flindex;
>> + } else {
>> + slindex = get_index_for_insert(block->size);
>> + flindex = slindex / BITS_PER_LONG;
>> + }
>>
>> block->link.prev_page = 0;
>> block->link.prev_offset = 0;
>> @@ -316,6 +321,10 @@ struct xv_pool *xv_create_pool(void)
>> if (!pool)
>> return NULL;
>>
>> + /* cache the first/second-level indices for PAGE_SIZE allocations */
>> + pagesize_slindex = get_index_for_insert(PAGE_SIZE);
>> + pagesize_flindex = pagesize_slindex / BITS_PER_LONG;
>
> Why is this in xv_create_pool(). AFAICT, it can be called multiple
> times if there's more than one zram device. Do we really need
> variables for these? They look like something GCC constant propagation
> should take care of if they would be defines or static inline
> functions.

It should have been a define rather than in xv_create_pool but as I read
more about GCC constant propagation and look at the get_index_for_insert
I believe that this patch is unnecessary. For sizes near PAGE_SIZE
(>XV_MAX_ALLOC_SIZE) I believe GCC constant propagation should do
exactly what I though I was trying to do. I will drop this patch.
Thank you for your reviews.