Re: [PATCH v2] mm/zswap: Check all pool pages instead of one pool pages

Cai Liu
2014-01-21T03:07:50Z

Thanks for your review.

2014/1/21 Minchan Kim <minchan@kernel.org>:
> Hello Cai,
>
> On Mon, Jan 20, 2014 at 03:50:18PM +0800, Cai Liu wrote:
>> zswap can support multiple swapfiles. So we need to check
>> all zbud pool pages in zswap.
>>
>> Version 2:
>> * add *total_zbud_pages* in zbud to record all the pages in pools
>> * move the updating of pool pages statistics to
>> alloc_zbud_page/free_zbud_page to hide the details
>>
>> Signed-off-by: Cai Liu <cai.liu@samsung.com>
>> ---
>> include/linux/zbud.h | 2 +-
>> mm/zbud.c | 44 ++++++++++++++++++++++++++++++++------------
>> mm/zswap.c | 4 ++--
>> 3 files changed, 35 insertions(+), 15 deletions(-)
>>
>> diff --git a/include/linux/zbud.h b/include/linux/zbud.h
>> index 2571a5c..1dbc13e 100644
>> --- a/include/linux/zbud.h
>> +++ b/include/linux/zbud.h
>> @@ -17,6 +17,6 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle);
>> int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries);
>> void *zbud_map(struct zbud_pool *pool, unsigned long handle);
>> void zbud_unmap(struct zbud_pool *pool, unsigned long handle);
>> -u64 zbud_get_pool_size(struct zbud_pool *pool);
>> +u64 zbud_get_pool_size(void);
>>
>> #endif /* _ZBUD_H_ */
>> diff --git a/mm/zbud.c b/mm/zbud.c
>> index 9451361..711aaf4 100644
>> --- a/mm/zbud.c
>> +++ b/mm/zbud.c
>> @@ -52,6 +52,13 @@
>> #include <linux/spinlock.h>
>> #include <linux/zbud.h>
>>
>> +/*********************************
>> +* statistics
>> +**********************************/
>> +
>> +/* zbud pages in all pools */
>> +static u64 total_zbud_pages;
>> +
>> /*****************
>> * Structures
>> *****************/
>> @@ -142,10 +149,28 @@ static struct zbud_header *init_zbud_page(struct page *page)
>> return zhdr;
>> }
>>
>> +static struct page *alloc_zbud_page(struct zbud_pool *pool, gfp_t gfp)
>> +{
>> + struct page *page;
>> +
>> + page = alloc_page(gfp);
>> +
>> + if (page) {
>> + pool->pages_nr++;
>> + total_zbud_pages++;
>
> Who protect race?

Yes, here the pool->pages_nr and also the total_zbud_pages are not protected.
I will re-do it.

I will change *total_zbud_pages* to atomic type.
For *pool->pages_nr*, one way is to use pool->lock to protect. But I
think it is too heavy.
So does it ok to change pages_nr to atomic type too?

>
>> + }
>> +
>> + return page;
>> +}
>> +
>> +
>> /* Resets the struct page fields and frees the page */
>> -static void free_zbud_page(struct zbud_header *zhdr)
>> +static void free_zbud_page(struct zbud_pool *pool, struct zbud_header *zhdr)
>> {
>> __free_page(virt_to_page(zhdr));
>> +
>> + pool->pages_nr--;
>> + total_zbud_pages--;
>> }
>>
>> /*
>> @@ -279,11 +304,10 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
>>
>> /* Couldn't find unbuddied zbud page, create new one */
>> spin_unlock(&pool->lock);
>> - page = alloc_page(gfp);
>> + page = alloc_zbud_page(pool, gfp);
>> if (!page)
>> return -ENOMEM;
>> spin_lock(&pool->lock);
>> - pool->pages_nr++;
>> zhdr = init_zbud_page(page);
>> bud = FIRST;
>>
>> @@ -349,8 +373,7 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle)
>> if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> /* zbud page is empty, free */
>> list_del(&zhdr->lru);
>> - free_zbud_page(zhdr);
>> - pool->pages_nr--;
>> + free_zbud_page(pool, zhdr);
>> } else {
>> /* Add to unbuddied list */
>> freechunks = num_free_chunks(zhdr);
>> @@ -447,8 +470,7 @@ next:
>> * Both buddies are now free, free the zbud page and
>> * return success.
>> */
>> - free_zbud_page(zhdr);
>> - pool->pages_nr--;
>> + free_zbud_page(pool, zhdr);
>> spin_unlock(&pool->lock);
>> return 0;
>> } else if (zhdr->first_chunks == 0 ||
>> @@ -496,14 +518,12 @@ void zbud_unmap(struct zbud_pool *pool, unsigned long handle)
>>
>> /**
>> * zbud_get_pool_size() - gets the zbud pool size in pages
>> - * @pool: pool whose size is being queried
>> *
>> - * Returns: size in pages of the given pool. The pool lock need not be
>> - * taken to access pages_nr.
>> + * Returns: size in pages of all the zbud pools.
>> */
>> -u64 zbud_get_pool_size(struct zbud_pool *pool)
>> +u64 zbud_get_pool_size(void)
>> {
>> - return pool->pages_nr;
>> + return total_zbud_pages;
>> }
>>
>> static int __init init_zbud(void)
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 5a63f78..ef44d9d 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -291,7 +291,7 @@ static void zswap_free_entry(struct zswap_tree *tree,
>> zbud_free(tree->pool, entry->handle);
>> zswap_entry_cache_free(entry);
>> atomic_dec(&zswap_stored_pages);
>> - zswap_pool_pages = zbud_get_pool_size(tree->pool);
>> + zswap_pool_pages = zbud_get_pool_size();
>> }
>>
>> /* caller must hold the tree lock */
>> @@ -716,7 +716,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>>
>> /* update stats */
>> atomic_inc(&zswap_stored_pages);
>> - zswap_pool_pages = zbud_get_pool_size(tree->pool);
>> + zswap_pool_pages = zbud_get_pool_size();
>>
>> return 0;
>>
>> --
>> 1.7.10.4
>>
>> --
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>
> --
> Kind regards,
> Minchan Kim