From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, x4mmm@yandex-team.ru,
        dilipbalaut@gmail.com, tndrwang@gmail.com,
        pgsql-hackers@lists.postgresql.org, tomas.vondra@enterprisedb.com
Subject: Re: SLRU optimization - configurable buffer pool and partitioning the
 SLRU lock
In-reply-to: <3885480.1709590472@sss.pgh.pa.us>
References: <202403031358.b435eh7u72td@alvherre.pgsql>
 <3885480.1709590472@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Mon, 04 Mar 2024 17:14:32 -0500"
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Date: Mon, 04 Mar 2024 17:41:58 -0500
Message-ID: <3898618.1709592118@sss.pgh.pa.us>
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 <https://www.postgresql.org/message-id/3898618.1709592118%40sss.pgh.pa.us>
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I wrote:
> It looks like SLRU_PAGE_EMPTY has (by chance, or deliberately)
> the numeric value of zero, so I guess the majority of our BF
> animals are understanding this as "address != NULL".  But that
> doesn't look like a useful test to be making.

In hopes of noticing whether there are other similar thinkos,
I permuted the order of the SlruPageStatus enum values, and
now I get the expected warnings from gcc:

In file included from ../../../../src/include/postgres.h:45,
                 from slru.c:59:
slru.c: In function ‘SimpleLruWaitIO’:
slru.c:436:38: warning: comparison between pointer and integer
  Assert(&shared->page_status[slotno] != SLRU_PAGE_EMPTY);
                                      ^~
../../../../src/include/c.h:862:9: note: in definition of macro ‘Assert’
   if (!(condition)) \
         ^~~~~~~~~
slru.c: In function ‘SimpleLruWritePage’:
slru.c:717:43: warning: comparison between pointer and integer
  Assert(&ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
                                           ^~
../../../../src/include/c.h:862:9: note: in definition of macro ‘Assert’
   if (!(condition)) \
         ^~~~~~~~~

So it looks like it's just these two places.

			regards, tom lane