add cc Seth 's new email address.

On Fri, Nov 8, 2013 at 6:28 PM, Bob Liu [off-list ref] wrote:

quoted

On 11/08/2013 05:50 PM, changkun.li wrote:

quoted

In zswap, store page A to zbud if the compression ratio is high, insert
its entry into rbtree. if there is a entry B which has the same offset
in the rbtree.Remove and free B before insert the entry of A.

case:
if the compression ratio of page A is not high, return without checking
the same offset one in rbtree.

if there is a entry B which has the same offset in the rbtree. Now, we
make sure B is invalid or expired. But the entry and compressed memory
of B are not freed in time.

Because zswap spaces data in memory, it makes the utilization of memory
lower. the other valid data in zbud is writeback to swap device more
possibility, when zswap is full.

So if we make sure a entry is expired, free it in time.

Signed-off-by: changkun.li<redacted>
---
 mm/zswap.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index cbd9578..90a2813 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c

@@ -596,6 +596,7 @@ fail:
      return ret;
 }

+static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t

offset);
 /*********************************
 * frontswap hooks
 **********************************/

@@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,

pgoff_t offset,

      if (!tree) {
              ret = -ENODEV;
-             goto reject;
+             goto nodev;
      }

      /* reclaim space if needed */

@@ -695,6 +696,8 @@ freepage:
      put_cpu_var(zswap_dstmem);
      zswap_entry_cache_free(entry);
 reject:
+     zswap_frontswap_invalidate_page(type, offset);

I'm afraid when arrives here zswap_rb_search(offset) will always return
NULL entry. So most of the time, it's just waste time to call
zswap_frontswap_invalidate_page() to search rbtree.

Yes, it is a bug.

But I agree with Bob, this patch is not efficient.

How about like this?

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 1b24bdc..1227896
--- a/mm/frontswap.c
+++ b/mm/frontswap.c

@@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
                  the (older) page from frontswap
                 */
                inc_frontswap_failed_stores();
-               if (dup)
+               if (dup) {
+                       frontswap_ops->invalidate_page(type, offset);
                        __frontswap_clear(sis, offset);
+               }
        }
        if (frontswap_writethrough_enabled)
                /* report failure so swap also writes to swap device */

quoted

--
Regards,
-Bob
--
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