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From: Michael Paquier <[email protected]>
To: Kyotaro Horiguchi <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: Set huge_page_size on 32bit system
Date: Fri, 26 Jun 2026 14:26:31 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAMp4U1d177Jf9ZJwXGKom6APx3LSFATa=Z-M=N5kLzvTUcxutw@mail.gmail.com>
	<[email protected]>

On Fri, Jun 26, 2026 at 01:24:15PM +0900, Kyotaro Horiguchi wrote:
> We could also make the later calculation use a wider integer type, but
> such a value would not be usable anyway on a platform where it does
> not fit in Size.  So it seems better to reject it earlier in
> check_huge_page_size(), before reaching CreateAnonymousSegment().

The top of guc.h includes the following thing:
/*
 * Maximum for integer GUC variables that are measured in kilobytes of memory.
 * This value is chosen to ensure that the corresponding number of bytes fits
 * into a variable of type size_t or ssize_t.  Be sure to compute the number
 * of bytes like "guc_var * (Size) 1024" to avoid int-width overflow.
 */
#if SIZEOF_SIZE_T > 4
#define MAX_KILOBYTES	INT_MAX
#else
#define MAX_KILOBYTES	(INT_MAX / 1024)
#endif

So it seems to me that the mistake is that huge_page_size uses INT_MAX
as upper bound.  We should use MAX_KILOBYTES instead; this definition
exists to exactly prevent this kind of computation mistake in 32b
environments.
--
Michael


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