Re: [PATCH] mm: extend zero pages to same element pages for zram

[zhouxianrong]

On 2017/2/7 10:54, Minchan Kim wrote:

On Tue, Feb 07, 2017 at 10:20:57AM +0800, zhouxianrong wrote:

< snip >

3. the below should be modified.

static inline bool zram_meta_get(struct zram *zram)
@@ -495,11 +553,17 @@ static void zram_meta_free(struct zram_meta *meta, u64 
disksize)

        /* Free all pages that are still in this zram device */
        for (index = 0; index < num_pages; index++) {
-               unsigned long handle = meta->table[index].handle;
+               unsigned long handle;
+
+               bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
+               handle = meta->table[index].handle;

-               if (!handle)
+               if (!handle || zram_test_flag(meta, index, ZRAM_SAME)) {
+                       bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
                        continue;
+               }

+               bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
                zs_free(meta->mem_pool, handle);

Could you explain why we need this modification?

        }

@@ -511,7 +575,7 @@ static void zram_meta_free(struct zram_meta *meta, u64 
disksize)
static struct zram_meta *zram_meta_alloc(char *pool_name, u64 disksize)
{
        size_t num_pages;
-       struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
+       struct zram_meta *meta = kzalloc(sizeof(*meta), GFP_KERNEL);

Ditto

.

because of union of handle and element, i think a non-zero element (other than 
handle) is prevented from freeing.
if zram_meta_get was modified, zram_meta_alloc did so.

Right. Thanks but I don't see why we need the locking in there and modification 
of
zram_meta_alloc.

Isn't it enough with this?

i am afraid someone do reset_store, so did lock.

yes, i am wrong, zram_meta_alloc should not be modified here. because 
meta->table has already cleared

        meta->table = vzalloc(num_pages * sizeof(*meta->table));

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index c20b05a84f21..a25d34a8af19 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -425,8 +425,11 @@ static void zram_meta_free(struct zram_meta *meta, u64 
disksize)
        /* Free all pages that are still in this zram device */
        for (index = 0; index < num_pages; index++) {
                unsigned long handle = meta->table[index].handle;
-
-               if (!handle)
+               /*
+                * No memory is allocated for same element filled pages.
+                * Simply clear same page flag.
+                */
+               if (!handle || zram_test_flag(meta, index, ZRAM_SAME))
                        continue;

                zs_free(meta->mem_pool, handle);

.