Re: Re: [PATCH 2/5] mm/readahead: Change the condition for SetPageReadahead

[Raghavendra D Prabhu <raghu.prabhu13@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1797 bytes --]

Hi,


* On Sat, Sep 22, 2012 at 08:49:20PM +0800, Fengguang Wu <fengguang.wu@intel.com> wrote:
>On Sat, Sep 22, 2012 at 04:03:11PM +0530, raghu.prabhu13@gmail.com wrote:
>> From: Raghavendra D Prabhu <rprabhu@wnohang.net>
>>
>> If page lookup from radix_tree_lookup is successful and its index page_idx ==
>> nr_to_read - lookahead_size, then SetPageReadahead never gets called, so this
>> fixes that.
>
>NAK. Sorry. It's actually an intentional behavior, so that for the
>common cases of many cached files that are accessed frequently, no
>PG_readahead will be set at all to pointlessly trap into the readahead
>routines once and again.

ACK, thanks for explaining that. However, regarding this, I would 
like to know if the implications of the patch 
51daa88ebd8e0d437289f589af29d4b39379ea76 will still apply if 
PG_readahead is not set.

>
>Perhaps we need a patch for commenting that case. :)
>
>Thanks,
>Fengguang
>
>> Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
>> ---
>>  mm/readahead.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/readahead.c b/mm/readahead.c
>> index 461fcc0..fec726c 100644
>> --- a/mm/readahead.c
>> +++ b/mm/readahead.c
>> @@ -189,8 +189,10 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
>>  			break;
>>  		page->index = page_offset;
>>  		list_add(&page->lru, &page_pool);
>> -		if (page_idx == nr_to_read - lookahead_size)
>> +		if (page_idx >= nr_to_read - lookahead_size) {
>>  			SetPageReadahead(page);
>> +			lookahead_size = 0;
>> +		}
>>  		ret++;
>>  	}
>>
>> --
>> 1.7.12.1
>




Regards,
-- 
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net

[-- Attachment #2: Type: application/pgp-signature, Size: 490 bytes --]