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From: "Yajun Deng" Message-ID: <57fda19f31d5fb7c6220ca679a969668@linux.dev> Subject: Re: [PATCH] mmzone: Introduce for_each_populated_zone_pgdat() To: "Matthew Wilcox" , "Andrew Morton" Cc: david@redhat.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org In-Reply-To: References: <20230424030756.1795926-1-yajun.deng@linux.dev> <20230424145823.b8e8435dd3242614371be6d5@linux-foundation.org> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ogd9oyb9wdhx71k15i36gwtbynjkryy8 X-Rspam-User: X-Rspamd-Queue-Id: 09087C000E X-Rspamd-Server: rspam06 X-HE-Tag: 1682404023-599887 X-HE-Meta: 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 gvw7RT1G F5ev5B9eb6U/60Ri1ZKQh7ZxwLhrvBODfQr71VMBCieiWPqloA/hXZPUM6sZIMNs3P9aXYF+zorsXtocFDS14Zl9+V53BSI2VWitl+p3ZC1jUBnLUJfV4Jqad2HaExIpKV7sVtKC1Y3Z1zM9qQ1C4zBAhIHijLdug+o14w2IHk47DI3eCQl7XnG2oXQSYxJX1C5pVI1cGNhmfhs+CZ/VecBhjwNqvF+HQvCXN9FUMbz7VhYA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: April 25, 2023 11:23 AM, "Matthew Wilcox" wrote:=0A= =0A> On Mon, Apr 24, 2023 at 02:58:23PM -0700, Andrew Morton wrote:=0A> = =0A>> On Mon, 24 Apr 2023 04:50:37 +0100 Matthew Wilcox wrote:=0A>> =0A>> On Mon, Apr 24, 2023 at 11:07:56AM +0800, Yajun De= ng wrote:=0A>>> Instead of define an index and determining if the zone ha= s memory,=0A>>> introduce for_each_populated_zone_pgdat() helper that can= be used=0A>>> to iterate over each populated zone in pgdat, and convert = the most=0A>>> obvious users to it.=0A>> =0A>> I don't think the complexi= ty of the helper justifies the simplification=0A>> of the users.=0A>> =0A= >> Are you sure?=0A>> =0A>>> +++ b/include/linux/mmzone.h=0A>>> @@ -1580,= 6 +1580,14 @@ extern struct zone *next_zone(struct zone *zone);=0A>>> ; /= * do nothing */ \=0A>>> else=0A>>> =0A>>> +#define for_each_populated_zon= e_pgdat(zone, pgdat, max) \=0A>>> + for (zone =3D pgdat->node_zones; \=0A= >>> + zone < pgdat->node_zones + max; \=0A>>> + zone++) \=0A>>> + if (!po= pulated_zone(zone)) \=0A>>> + ; /* do nothing */ \=0A>>> + else=0A>>> += =0A>> =0A>> But each of the call sites is doing this, so at least the com= plexity is=0A>> now seen in only one place.=0A> =0A> But they're not doin= g _that_. They're doing something normal and=0A> obvious like:=0A> =0A> f= or (zone =3D pgdat->node_zones; zone < pgdat->node_zones + max; zone++) {= =0A> if (!populated_zone(zone)=0A> continue;=0A> ...=0A> }=0A>=0A=0AThey = will be like:=0A=0Afor (zone =3D pgdat->node_zones; zone < pgdat->node_zo= nes + max; zone++)=0A if (!populated_zone(zone))=0A = ;=0A else {=0A=0A ...=0A }=0A =0A =0A> = which clearly does what it's supposed to. But with this patch, there's=0A= > macro expansion involved, and it's not a nice simple macro, it has a lo= op=0A> _and_ an if-condition, and there's an else, and now I have to thin= k hard=0A> about whether flow control is going to do the right thing if t= he body=0A> of the loop isn't simple.=0A> =0A>> btw, do we need to do the= test that way? Why won't this work?=0A>> =0A>> #define for_each_populate= d_zone_pgdat(zone, pgdat, max) \=0A>> for (zone =3D pgdat->node_zones; \= =0A>> zone < pgdat->node_zones + max; \=0A>> zone++) \=0A>> if (populated= _zone(zone))=0A> =0A> I think it will work, except that this is now legal= :=0A> =0A> for_each_populated_zone_pgdat(zone, pgdat, 3)=0A> else i++;=0A= > =0A> and really, I think that demonstrates why we don't want macros tha= t are=0A> that darn clever.