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

[zhouxianrong]

On 2017/2/5 22:21, Minchan Kim wrote:
> Hi zhouxianrong,
>
> On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@xxxxxxxxxx wrote:
> > From: zhouxianrong <zhouxianrong@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >  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.

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?

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);
 	}

@@ -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);