From: Raghavendra D Prabhu <raghu.prabhu13@gmail.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: linux-mm@kvack.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org
Subject: Re: Re: Re: [PATCH 2/5] mm/readahead: Change the condition for SetPageReadahead
Date: Tue, 16 Oct 2012 23:12:52 +0530 [thread overview]
Message-ID: <20121016174252.GB2826@Archie> (raw)
In-Reply-To: <20120928115623.GB1525@localhost>
[-- Attachment #1: Type: text/plain, Size: 2127 bytes --]
Hi,
* On Fri, Sep 28, 2012 at 07:56:23PM +0800, Fengguang Wu <fengguang.wu@intel.com> wrote:
>On Wed, Sep 26, 2012 at 06:59:00AM +0530, Raghavendra D Prabhu wrote:
>> 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.
>
>Would you elaborate the implication and the possible problematic case?
Certainly.
An implication of 51daa88ebd8e0d437289f589af29d4b39379ea76 is
that, a redundant check for PageReadahead(page) is avoided since
async is piggy-backed into the synchronous readahead itself.
So, in case of
page = find_get_page()
if(!page)
page_cache_sync_readahead()
else if (PageReadahead(page))
page_cache_async_readahead();
isnt' there a possibility that PG_readahead won't be set at all
if page is not in cache (causing page_cache_sync_readahead) but
page at index (nr_to_read - lookahead_size) is already in the
cache? (due to if (page) continue; in the code)?
Hence, I changed the condition from equality to >= for setting
SetPageReadahead(page) (and added a
variable so that it is done only once).
>
>Thanks,
>Fengguang
>
Regards,
--
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net
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next prev parent reply other threads:[~2012-10-16 17:42 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-22 10:33 [PATCH 0/5] Readahead fixes / improvements raghu.prabhu13
[not found] ` <cover.1348309711.git.rprabhu@wnohang.net>
2012-09-22 10:33 ` [PATCH 1/5] mm/readahead: Check return value of read_pages raghu.prabhu13
2012-09-22 12:43 ` Fengguang Wu
2012-09-26 1:25 ` Raghavendra D Prabhu
2012-09-28 11:54 ` Fengguang Wu
2012-10-16 17:47 ` Raghavendra D Prabhu
2012-10-17 2:53 ` Fengguang Wu
2012-09-22 10:33 ` [PATCH 2/5] mm/readahead: Change the condition for SetPageReadahead raghu.prabhu13
2012-09-22 12:49 ` Fengguang Wu
2012-09-26 1:29 ` Raghavendra D Prabhu
2012-09-28 11:56 ` Fengguang Wu
2012-10-16 17:42 ` Raghavendra D Prabhu [this message]
2012-10-17 2:34 ` Fengguang Wu
2012-09-22 10:33 ` [PATCH 3/5] Remove file_ra_state from arguments of count_history_pages raghu.prabhu13
2012-09-22 12:40 ` Fengguang Wu
2012-10-16 18:21 ` Raghavendra D Prabhu
2012-10-17 3:15 ` Fengguang Wu
2012-09-22 10:33 ` [PATCH 4/5] Move the check for ra_pages after VM_SequentialReadHint() raghu.prabhu13
2012-09-22 12:42 ` Fengguang Wu
2012-09-26 1:39 ` Raghavendra D Prabhu
2012-10-16 18:15 ` Raghavendra D Prabhu
2012-10-17 3:13 ` Fengguang Wu
2012-09-22 10:33 ` [PATCH 5/5] mm/readahead: Use find_get_pages instead of radix_tree_lookup raghu.prabhu13
2012-09-22 13:15 ` Fengguang Wu
2012-09-26 2:58 ` Raghavendra D Prabhu
2012-09-28 12:18 ` Fengguang Wu
2012-10-16 16:59 ` Raghavendra D Prabhu
2012-10-17 2:12 ` Fengguang Wu
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