Hello Bob,
On Tue, Jan 14, 2014 at 09:19:23AM +0800, Bob Liu wrote:
>
> On 01/14/2014 07:35 AM, Minchan Kim wrote:
> > Hello,
> >
> > On Sat, Jan 11, 2014 at 03:43:07PM +0800, Cai Liu wrote:
> >> zswap can support multiple swapfiles. So we need to check
> >> all zbud pool pages in zswap.
> >
> > True but this patch is rather costly that we should iterate
> > zswap_tree[MAX_SWAPFILES] to check it. SIGH.
> >
> > How about defining zswap_tress as linked list instead of static
> > array? Then, we could reduce unnecessary iteration too much.
> >
>
> But if use linked list, it might not easy to access the tree like this:
> struct zswap_tree *tree = zswap_trees[type];
struct zswap_tree {
..
..
struct list_head list;
}
zswap_frontswap_init()
{
..
..
zswap_trees[type] = tree;
list_add(&tree->list, &zswap_list);
}
get_zswap_pool_pages(void)
{
struct zswap_tree *cur;
list_for_each_entry(cur, &zswap_list, list) {
pool_pages += zbud_get_pool_size(cur->pool);
}
return pool_pages;
}
>
> BTW: I'm still prefer to use dynamic pool size, instead of use
> zswap_is_full(). AFAIR, Seth has a plan to replace the rbtree with radix
> which will be more flexible to support this feature and page migration
> as well.
>
> > Other question:
> > Why do we need to update zswap_pool_pages too frequently?
> > As I read the code, I think it's okay to update it only when user
> > want to see it by debugfs and zswap_is_full is called.
> > So could we optimize it out?
> >
> >>
> >> Signed-off-by: Cai Liu <cai....@samsung.com>
>
> Reviewed-by: Bob Liu <bob....@oracle.com>
Hmm, I really suprised you are okay in this code piece where we have
unnecessary cost most of case(ie, most system has a swap device) in
*mm* part.
Anyway, I don't want to merge this patchset.
If Andrew merge it and anybody doesn't do right work, I will send a patch.
Cai, Could you redo a patch?
I don't want to intercept your credit.
Even, we could optimize to reduce the the number of call as I said in
previous reply.
Thanks.
>
> >> ---
> >> mm/zswap.c | 18 +++++++++++++++---
> >> 1 file changed, 15 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/mm/zswap.c b/mm/zswap.c
> >> index d93afa6..2438344 100644
> >> --- a/mm/zswap.c
> >> +++ b/mm/zswap.c
> >> @@ -291,7 +291,6 @@ 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);
> >> }
> >>
> >> /* caller must hold the tree lock */
> >> @@ -405,10 +404,24 @@ cleanup:
> >> /*********************************
> >> * helpers
> >> **********************************/
> >> +static u64 get_zswap_pool_pages(void)
> >> +{
> >> + int i;
> >> + u64 pool_pages = 0;
> >> +
> >> + for (i = 0; i < MAX_SWAPFILES; i++) {
> >> + if (zswap_trees[i])
> >> + pool_pages += zbud_get_pool_size(zswap_trees[i]->pool);
> >> + }
> >> + zswap_pool_pages = pool_pages;
> >> +
> >> + return pool_pages;
> >> +}
> >> +
> >> static bool zswap_is_full(void)
> >> {
> >> return (totalram_pages * zswap_max_pool_percent / 100 <
> >> - zswap_pool_pages);
> >> + get_zswap_pool_pages());
> >> }
> >>
> >> /*********************************
> >> @@ -716,7 +729,6 @@ 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);
> >>
> >> return 0;
> >>
> >> --
> >> 1.7.10.4
> --
> Regards,
> -Bob
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majord...@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a>
--
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
