LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Tejun Heo <tj@kernel.org>
To: Mike Snitzer <snitzer@redhat.com>
Cc: axboe@kernel.dk, tytso@mit.edu, djwong@us.ibm.com,
	shli@kernel.org, neilb@suse.de, adilger.kernel@dilger.ca,
	jack@suse.cz, linux-kernel@vger.kernel.org, kmannth@us.ibm.com,
	cmm@us.ibm.com, linux-ext4@vger.kernel.org, rwheeler@redhat.com,
	hch@lst.de, josef@redhat.com, jmoyer@redhat.com
Subject: Re: [RFC PATCH 4/3] block: skip elevator initialization for flush requests
Date: Tue, 1 Feb 2011 19:52:25 +0100	[thread overview]
Message-ID: <20110201185225.GT14211@htj.dyndns.org> (raw)
In-Reply-To: <20110201173846.GA25252@redhat.com>

Hello,

On Tue, Feb 01, 2011 at 12:38:46PM -0500, Mike Snitzer wrote:
> > I thought about doing it this way but I think we're burying the
> > REQ_FLUSH|REQ_FUA test logic too deep.  get_request() shouldn't
> > "magically" know not to allocate elevator data.
> 
> There is already a considerable amount of REQ_FLUSH|REQ_FUA special
> casing magic sprinkled though-out the block layer.  Why is this
> get_request() change the case that goes too far?

After the reimplementation, FLUSH implementation seems to be pretty
well isolated.  Also, having REQ_FLUSH logic in the issue and
completion paths is logical and preventing them from leaking to other
places sounds like a good idea.

> > The decision should
> > be made higher in the stack and passed down to get_request().  e.g. if
> > REQ_SORTED is set in @rw, elevator data is allocated; otherwise, not.
> 
> Considering REQ_SORTED is set in elv_insert(), well after get_request() 
> is called, I'm not seeing what you're suggesting.

I was suggesting using REQ_SORTED in @rw parameter to indicate "this
request may be sorted and thus needs elevator data allocation".

> Anyway, I agree that ideally we'd have a mechanism to explicitly
> short-circuit elevator initialization.  But doing so in a meaningful way
> would likely require a fair amount of refactoring of get_request* and
> its callers.  I'll come back to this and have another look but my gut is
> this interface churn wouldn't _really_ help -- all things considered.

I don't know.  I agree that it's not a critical issue but, to me,
subjectively of course, it feels a bit too subtle.  The sharing of
fields using unions is already subtle enough.  I with that at least
the allocation switching would be obvious and explicit.  The combined
subtleties scare me.

Thank you.

-- 
tejun

  reply	other threads:[~2011-02-01 18:52 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-21 15:59 [PATCHSET] block: reimplement FLUSH/FUA to support merge Tejun Heo
2011-01-21 15:59 ` [PATCH 1/3] block: add REQ_FLUSH_SEQ Tejun Heo
2011-01-21 15:59 ` [PATCH 2/3] block: improve flush bio completion Tejun Heo
2011-01-21 15:59 ` [PATCH 3/3] block: reimplement FLUSH/FUA to support merge Tejun Heo
2011-01-21 18:56   ` Vivek Goyal
2011-01-21 19:19     ` Vivek Goyal
2011-01-23 10:25     ` Tejun Heo
2011-01-23 10:29       ` Tejun Heo
2011-01-24 20:31       ` Darrick J. Wong
2011-01-25 10:21         ` Tejun Heo
2011-01-25 11:39           ` Jens Axboe
2011-03-23 23:37             ` Darrick J. Wong
2011-01-25 22:56           ` Darrick J. Wong
2011-01-22  0:49   ` Mike Snitzer
2011-01-23 10:31     ` Tejun Heo
2011-01-25 20:46       ` Vivek Goyal
2011-01-25 21:04         ` Mike Snitzer
2011-01-23 10:48   ` [PATCH UPDATED " Tejun Heo
2011-01-25 20:41   ` [KNOWN BUGGY RFC PATCH 4/3] block: skip elevator initialization for flush requests Mike Snitzer
2011-01-25 21:55     ` Mike Snitzer
2011-01-26  5:27       ` [RFC PATCH 4/3] block: skip elevator initialization for flush requests -- was never BUGGY relative to upstream Mike Snitzer
2011-01-26 10:03     ` [KNOWN BUGGY RFC PATCH 4/3] block: skip elevator initialization for flush requests Tejun Heo
2011-01-26 10:05       ` Tejun Heo
2011-02-01 17:38       ` [RFC " Mike Snitzer
2011-02-01 18:52         ` Tejun Heo [this message]
2011-02-01 22:46           ` [PATCH v2 1/2] " Mike Snitzer
2011-02-02 21:51             ` Vivek Goyal
2011-02-02 22:06               ` Mike Snitzer
2011-02-02 22:55             ` [PATCH v3 1/2] block: skip elevator data " Mike Snitzer
2011-02-03  9:28               ` Tejun Heo
2011-02-03 14:48                 ` [PATCH v4 " Mike Snitzer
2011-02-03 13:24               ` [PATCH v3 " Jens Axboe
2011-02-03 13:38                 ` Tejun Heo
2011-02-04 15:04                   ` Vivek Goyal
2011-02-04 15:08                     ` Tejun Heo
2011-02-04 16:58                     ` [PATCH v5 " Mike Snitzer
2011-02-03 14:54                 ` [PATCH v3 " Mike Snitzer
2011-02-01 22:46           ` [PATCH v2 2/2] block: share request flush fields with elevator_private Mike Snitzer
2011-02-02 21:52             ` Vivek Goyal
2011-02-03  9:24             ` Tejun Heo
2011-02-11 10:08             ` Jens Axboe

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=20110201185225.GT14211@htj.dyndns.org \
    --to=tj@kernel.org \
    --cc=adilger.kernel@dilger.ca \
    --cc=axboe@kernel.dk \
    --cc=cmm@us.ibm.com \
    --cc=djwong@us.ibm.com \
    --cc=hch@lst.de \
    --cc=jack@suse.cz \
    --cc=jmoyer@redhat.com \
    --cc=josef@redhat.com \
    --cc=kmannth@us.ibm.com \
    --cc=linux-ext4@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=neilb@suse.de \
    --cc=rwheeler@redhat.com \
    --cc=shli@kernel.org \
    --cc=snitzer@redhat.com \
    --cc=tytso@mit.edu \
    --subject='Re: [RFC PATCH 4/3] block: skip elevator initialization for flush requests' \
    /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

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).