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Message-ID: <ba64f168-72f5-65c3-c88c-7a59e57b20aa@huawei.com>
Date: Tue, 7 Feb 2017 10:20:57 +0800
From: zhouxianrong <zhouxianrong@...wei.com>
To: Minchan Kim <minchan@...nel.org>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
<akpm@...ux-foundation.org>, <sergey.senozhatsky@...il.com>,
<willy@...radead.org>, <iamjoonsoo.kim@....com>,
<ngupta@...are.org>, <Mi.Sophia.Wang@...wei.com>,
<zhouxiyu@...wei.com>, <weidu.du@...wei.com>,
<zhangshiming5@...wei.com>, <won.ho.park@...wei.com>
Subject: Re: [PATCH] mm: extend zero pages to same element pages for zram
On 2017/2/7 7:48, Minchan Kim wrote:
> 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@...wei.com wrote:
>>>> From: zhouxianrong <zhouxianrong@...wei.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@...wei.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.
yes, Matthew is right, thanks
>
>>
>> 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.
yes
>
>>
>> 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.
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