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

On Mon, Feb 06, 2017 at 09:28:18AM +0800, zhouxianrong wrote:
>
>
> On 2017/2/5 22:21, Minchan Kim wrote:
> >Hi zhouxianrong,
> >
> >On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@huawei.com wrote:
> >>From: zhouxianrong <zhouxianrong@huawei.com>
> >>
> >>test result as listed below:
> >>
> >>zero pattern_char pattern_short pattern_int pattern_long total (unit)
> >>162989 14454 3534 23516 2769 3294399 (page)
> >>
> >>statistics for the result:
> >>
> >> zero pattern_char pattern_short pattern_int pattern_long
> >>AVERAGE 0.745696298 0.085937175 0.015957701 0.131874915 0.020533911
> >>STDEV 0.035623777 0.016892402 0.004454534 0.021657123 0.019420072
> >>MAX 0.973813421 0.222222222 0.021409518 0.211812245 0.176512625
> >>MIN 0.645431905 0.004634398 0 0 0
> >
> >The description in old version was better for justifying same page merging
> >feature.
> >
> >>
> >>Signed-off-by: zhouxianrong <zhouxianrong@huawei.com>
> >>---
> >> drivers/block/zram/zram_drv.c | 124 +++++++++++++++++++++++++++++++----------
> >> drivers/block/zram/zram_drv.h | 11 ++--
> >> 2 files changed, 103 insertions(+), 32 deletions(-)
> >>
> >>diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> >>index e5ab7d9..6a8c9c5 100644
> >>--- a/drivers/block/zram/zram_drv.c
> >>+++ b/drivers/block/zram/zram_drv.c
> >>@@ -95,6 +95,17 @@ static void zram_clear_flag(struct zram_meta *meta, u32 index,
> >> meta->table[index].value &= ~BIT(flag);
> >> }
> >>
> >>+static inline void zram_set_element(struct zram_meta *meta, u32 index,
> >>+ unsigned long element)
> >>+{
> >>+ meta->table[index].element = element;
> >>+}
> >>+
> >>+static inline void zram_clear_element(struct zram_meta *meta, u32 index)
> >>+{
> >>+ meta->table[index].element = 0;
> >>+}
> >>+
> >> static size_t zram_get_obj_size(struct zram_meta *meta, u32 index)
> >> {
> >> return meta->table[index].value & (BIT(ZRAM_FLAG_SHIFT) - 1);
> >>@@ -167,31 +178,78 @@ static inline void update_used_max(struct zram *zram,
> >> } while (old_max != cur_max);
> >> }
> >>
> >>-static bool page_zero_filled(void *ptr)
> >>+static inline void zram_fill_page(char *ptr, unsigned long value)
> >>+{
> >>+ int i;
> >>+ unsigned long *page = (unsigned long *)ptr;
> >>+
> >>+ if (likely(value == 0)) {
> >>+ clear_page(ptr);
> >>+ } else {
> >>+ for (i = 0; i < PAGE_SIZE / sizeof(*page); i++)
> >>+ page[i] = value;
> >>+ }
> >>+}
> >>+
> >>+static inline void zram_fill_page_partial(char *ptr, unsigned int size,
> >>+ unsigned long value)
> >>+{
> >>+ int i;
> >>+ unsigned long *page;
> >>+
> >>+ if (likely(value == 0)) {
> >>+ memset(ptr, 0, size);
> >>+ return;
> >>+ }
> >>+
> >>+ i = ((unsigned long)ptr) % sizeof(*page);
> >>+ if (i) {
> >>+ while (i < sizeof(*page)) {
> >>+ *ptr++ = (value >> (i * 8)) & 0xff;
> >>+ --size;
> >>+ ++i;
> >>+ }
> >>+ }
> >>+
> >
> >I don't think we need this part because block layer works with sector
> >size or multiple times of it so it must be aligned unsigned long.
> >
> >
> >
> >
> >.
> >
>
> Minchan and Matthew Wilcox:
>
> 1. right, but users could open /dev/block/zram0 file and do any read operations.

Could you make that happen?
I don't think it's possible as Matthew already pointed out, too.

>
> 2. about endian operation for long, the modification is trivial and low efficient.
> i have not better method. do you have any good idea for this?

So if assumption 1 is wrong, we don't need 2, either.

>
> 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

>
>

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