Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag

From: Pavel Machek <pavel@ucw.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Neil Brown <neilb@suse.de>,
	Theodore Ts'o <tytso@mit.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag
Date: Thu, 31 Aug 2017 11:10:25 +0200	[thread overview]
Message-ID: <20170831091024.GB12920@amd> (raw)
In-Reply-To: <20170828123542.GJ17097@dhcp22.suse.cz>

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Hi!

> > > > You can define more exact meaning, and then adjust the usage. But
> > > > there's no need to do treewide replacement...
> > > 
> > > I have checked most of them and except for the initially added onces the
> > > large portion where added without a good reasons or even break an
> > > intuitive meaning by taking locks.
> > 
> > I don't see it. kmalloc() itself takes locks. Of course everyone takes
> > locks. I don't think that's intuitive meaning.
> 
> I was talking about users of the flag. I have seen some to take a lock
> right after they allocated GFP_TEMPORARY object.

Yes, I'd expect people to take locks after allocating temporary
objects. kmalloc itself takes locks. If the allocation is "usually"
freed within miliseconds, that should be enough.

> > > Seriously, if we need a short term semantic it should be clearly defined
> > > first.
> > 
> > "milliseconds, not hours."
> > 
> > > Is there any specific case why you think this patch is in a wrong
> > > direction? E.g. a measurable regression?
> > 
> > Not playing that game. You should argue why it is improvement. And I
> > don't believe you did.
> 
> Please read the whole changelog where I was quite verbose about how the
> current flag is abused and how its semantic is weak and encourages a
> wrong usage pattern. Moreover it is not even clear whether it helps
> anything. I haven't seen any actual counter argument from you other than
> "milliseconds not hours" without actually explaining how that would be
> useful for any decisions done in the core MM layer.

Well, I find that argumentation insufficient for global
search&replace.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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