Date: Mon, 9 Aug 2021 20:42:05 -0700
From: Andres Freund <andres@anarazel.de>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Don Seiler <don@seiler.us>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Estimating HugePages Requirements?
Message-ID: <20210810034205.r72j5uouynepj4f2@alap3.anarazel.de>
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 <73A4E25F-1039-4FC9-8E6E-0A00230BDFB8@enterprisedb.com>
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Hi,

On 2021-08-09 22:57:18 +0000, Bossart, Nathan wrote:

> @@ -1026,6 +1031,18 @@ PostmasterMain(int argc, char *argv[])
>  	 */
>  	InitializeMaxBackends();
>  
> +	if (output_shmem)
> +	{
> +		char output[64];
> +		Size size;
> +
> +		size = CreateSharedMemoryAndSemaphores(true);
> +		sprintf(output, "%zu", size);
> +
> +		puts(output);
> +		ExitPostmaster(0);
> +	}

I don't like putting this into PostmasterMain(). Either BootstrapMain()
(specifically checker mode) or GucInfoMain() seem like better places.


> -void
> -CreateSharedMemoryAndSemaphores(void)
> +Size
> +CreateSharedMemoryAndSemaphores(bool size_only)
>  {
>  	PGShmemHeader *shim = NULL;
>  
> @@ -161,6 +161,9 @@ CreateSharedMemoryAndSemaphores(void)
>  		/* might as well round it off to a multiple of a typical page size */
>  		size = add_size(size, 8192 - (size % 8192));
>  
> +		if (size_only)
> +			return size;
> +
>  		elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
>  
>  		/*
> @@ -288,4 +291,6 @@ CreateSharedMemoryAndSemaphores(void)
>  	 */
>  	if (shmem_startup_hook)
>  		shmem_startup_hook();
> +
> +	return 0;
>  }

That seems like an ugly API to me. Why don't we split the size
determination and shmem creation functions into two?


Greetings,

Andres Freund