linux-kernel - Re: [RFC PATCH] treewide: remove GFP

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Message-ID: <20170825213936.GA13576@amd>
Date:   Fri, 25 Aug 2017 23:39:36 +0200
From:   Pavel Machek <pavel@....cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Neil Brown <neilb@...e.de>,
        Theodore Ts'o <tytso@....edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag

On Fri 2017-08-25 10:04:42, Michal Hocko wrote:
> On Fri 25-08-17 09:28:19, Pavel Machek wrote:
> > On Fri 2017-08-25 08:35:46, Michal Hocko wrote:
> > > On Wed 23-08-17 19:57:09, Pavel Machek wrote:
> [...]
> > > > Dunno. < 1msec probably is temporary, 1 hour probably is not. If it causes
> > > > problems, can you just #define GFP_TEMPORARY GFP_KERNEL ? Treewide replace,
> > > > and then starting again goes not look attractive to me.
> > > 
> > > I do not think we want a highlevel GFP_TEMPORARY without any meaning.
> > > This just supports spreading the flag usage without a clear semantic
> > > and it will lead to even bigger mess. Once we can actually define what
> > > the flag means we can also add its users based on that new semantic.
> > 
> > It has real meaning.
> 
> Which is?

"This allocation is temporary. It lasts milliseconds, not hours."

> > 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.

> 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.

Best regards,

								Pavel

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

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