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SubjectRe: [PATCH 4/6] staging: erofs: cleanup `z_erofs_vle_normalaccess_readpages'
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Hi Xiang,

On 2018/9/19 23:32, Gao Xiang wrote:
> Hi Chao,
>
> On 2018/9/19 23:26, Chao Yu wrote:
>> Hi Xiang,
>>
>> On 2018/9/19 13:49, Gao Xiang wrote:
>>> This patch introduces `__should_decompress_synchronously' to
>>> cleanup `z_erofs_vle_normalaccess_readpages'.
>>>
>>> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
>>> ---
>>> drivers/staging/erofs/internal.h | 11 +++++++++++
>>> drivers/staging/erofs/super.c | 5 +++++
>>> drivers/staging/erofs/unzip_vle.c | 20 ++++++--------------
>>> 3 files changed, 22 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
>>> index cfcc6db..c84eb97 100644
>>> --- a/drivers/staging/erofs/internal.h
>>> +++ b/drivers/staging/erofs/internal.h
>>> @@ -95,6 +95,9 @@ struct erofs_sb_info {
>>> /* the dedicated workstation for compression */
>>> struct radix_tree_root workstn_tree;
>>>
>>> + /* threshold for decompression synchronously */
>>> + unsigned int max_sync_decompress_pages;
>>> +
>>> #ifdef EROFS_FS_HAS_MANAGED_CACHE
>>> struct inode *managed_cache;
>>> #endif
>>> @@ -273,6 +276,14 @@ extern int erofs_try_to_free_cached_page(struct address_space *mapping,
>>> struct page *page);
>>> #endif
>>>
>>> +#define DEFAULT_MAX_SYNC_DECOMPRESS_PAGES 4
>>> +
>>> +static inline bool __should_decompress_synchronously(struct erofs_sb_info *sbi,
>>> + unsigned int nr)
>>> +{
>>> + return nr <= sbi->max_sync_decompress_pages;
>> - nr_pages < 4 /* sync */);
>>
>> There is a little bit changed except cleanup, IIUC, would it be any difference
>> of performance around boundary of four pages?
>
> No.. Once synchronous decompression is applied for 1,2,3 pages for no special reasons.
> But I think it could be better to adjust it to the power of two --- 1,2,3,4 is preferred.
> Since I have no idea to measure which is better or what value is best for all platform or use cases...
>
> Therefore I tune it in this patch since I don't like the number
> DEFAULT_MAX_SYNC_DECOMPRESS_PAGES == 3 ...

Yeah, how about adding one more patch to tune this magic number first? as that
change would not be part of cleanup thing. I guess later maybe we could export a
sysfs node to provider tuning ability on that threshold.

Thanks,

>
> Thanks,
> Gao Xiang
>
>>
>> Thanks,
>>

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