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

From	zhouxianrong <zhouxianrong@huawei.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm: extend zero pages to same element pages for zram
Date	2017-02-07 04:30 +0100
Message-ID	<t84DE-5EP-3@gated-at.bofh.it> (permalink)
References	(2 earlier) <t7vZf-8vP-5@gated-at.bofh.it> <t7GrD-6Dt-1@gated-at.bofh.it> <t81cJ-3ij-7@gated-at.bofh.it> <t83HA-4X1-9@gated-at.bofh.it> <t84aC-58r-15@gated-at.bofh.it>
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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);
>
> .
>

Thread

[PATCH] mm: extend zero pages to same element pages for zram <zhouxianrong@huawei.com> - 2017-02-03 09:50 +0100
  Re: [PATCH] mm: extend zero pages to same element pages for zram Matthew Wilcox <willy@infradead.org> - 2017-02-03 16:50 +0100
    Re: [PATCH] mm: extend zero pages to same element pages for zram zhouxianrong <zhouxianrong@huawei.com> - 2017-02-04 04:40 +0100
  Re: [PATCH] mm: extend zero pages to same element pages for zram Minchan Kim <minchan@kernel.org> - 2017-02-05 15:30 +0100
    Re: [PATCH] mm: extend zero pages to same element pages for zram zhouxianrong <zhouxianrong@huawei.com> - 2017-02-06 02:40 +0100
      Re: [PATCH] mm: extend zero pages to same element pages for zram Matthew Wilcox <willy@infradead.org> - 2017-02-06 15:20 +0100
      Re: [PATCH] mm: extend zero pages to same element pages for zram Minchan Kim <minchan@kernel.org> - 2017-02-07 00:50 +0100
        Re: [PATCH] mm: extend zero pages to same element pages for zram zhouxianrong <zhouxianrong@huawei.com> - 2017-02-07 03:30 +0100
          Re: [PATCH] mm: extend zero pages to same element pages for zram Minchan Kim <minchan@kernel.org> - 2017-02-07 04:00 +0100
            Re: [PATCH] mm: extend zero pages to same element pages for zram zhouxianrong <zhouxianrong@huawei.com> - 2017-02-07 04:30 +0100
              Re: [PATCH] mm: extend zero pages to same element pages for zram Minchan Kim <minchan@kernel.org> - 2017-02-07 06:00 +0100

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