linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Huang Ying <ying.huang@intel.com>,
	Jin Dongming <jin.dongming@np.css.fujitsu.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] Check whether pages are poisoned before copying
Date: Thu, 17 Mar 2011 16:43:03 +0900	[thread overview]
Message-ID: <4D81BB87.10803@jp.fujitsu.com> (raw)
In-Reply-To: <20110317062612.GE11094@one.firstfloor.org>

(2011/03/17 15:26), Andi Kleen wrote:
> On Thu, Mar 17, 2011 at 02:20:42PM +0900, Hidetoshi Seto wrote:
>> (2011/03/17 13:14), Andi Kleen wrote:
>>> On Thu, Mar 17, 2011 at 11:32:55AM +0900, Hidetoshi Seto wrote:
>>>> So to avoid the above problem, add poison checks for both of 4K pages
>>>> and the THP before copying in __collapse_huge_page_copy().
>>>
>>> I don't think you need the check for the huge page -- it should not be allocated
>>> in this case.
>>
>> Is there no case that the THP is once allocated but poison flag
>> is set before copy?  Though I know it is one of corner cases,
>> having this check for THP is worse than nothing.
> 
> There's a theoretical window, but it's only a few instructions.
> Probably not worth caring about, especially since you have a similar
> window after your check again.

At least copy to the last page of the huge page is performed after
all preceding copies are finished.  So I'm not sure it is really
"a few" or not.
Still I think making the window smaller than now is worthwhile,
no matter it is change from 0.1% to 0.01%, or from 0.01% to 0.001%.

Or did you find the downside of the check here?


Thanks,
H.Seto


  reply	other threads:[~2011-03-17  7:43 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-17  2:30 [PATCH 0/4] THP: page collapsing vs. poisoning Hidetoshi Seto
2011-03-17  2:31 ` [PATCH 1/4] Lock the new THP when collapsing pages Hidetoshi Seto
2011-03-17  2:32 ` [PATCH 2/4] Free the collapsed pages after the new THP is mapped Hidetoshi Seto
2011-03-17  2:32 ` [PATCH 3/4] Check whether pages are poisoned before copying Hidetoshi Seto
2011-03-17  4:14   ` Andi Kleen
2011-03-17  5:20     ` Hidetoshi Seto
2011-03-17  6:26       ` Andi Kleen
2011-03-17  7:43         ` Hidetoshi Seto [this message]
2011-03-17 14:04           ` Andrea Arcangeli
2011-03-17 15:25             ` Andi Kleen
2011-03-17 16:12               ` Andrea Arcangeli
2011-03-17 16:27                 ` Andi Kleen
2011-03-17 16:47                   ` Andrea Arcangeli
2011-03-17 22:55                     ` Andi Kleen
2011-03-23 17:26             ` K.Prasad
2011-03-23 17:32               ` Andi Kleen
2011-03-17 15:21           ` Andi Kleen
2011-03-18  5:26             ` Jin Dongming
2011-03-17  2:33 ` [PATCH 4/4] Check whether the new THP is poisoned before it is mapped to APL Hidetoshi Seto

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=4D81BB87.10803@jp.fujitsu.com \
    --to=seto.hidetoshi@jp.fujitsu.com \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=andi@firstfloor.org \
    --cc=jin.dongming@np.css.fujitsu.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ying.huang@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).