Commit39715af

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Fix broken mmap failure-detection code, and improve error message.

Per an observation by Thom Brown that my previous commit made anoverly large shmem allocation crash the server, on Linux.

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+10

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Lines changed: 10 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -419,10 +419,17 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)`
`419`	`419`	`*/`
`420`	`420`	`AnonymousShmem=mmap(NULL,size,PROT_READ\|PROT_WRITE,PG_MMAP_FLAGS,`
`421`	`421`	`-1,0);`
`422`		`-if (AnonymousShmem==NULL)`
	`422`	`+if (AnonymousShmem==MAP_FAILED)`
`423`	`423`	`ereport(FATAL,`
`424`		`- (errmsg("could not map %lu bytes of anonymous shared memory: %m",`
`425`		`-(unsigned long)AnonymousShmemSize)));`
	`424`	`+ (errmsg("could not map anonymous shared memory: %m"),`
	`425`	`+ (errno==ENOMEM) ?`
	`426`	`+errhint("This error usually means that PostgreSQL's request "`
	`427`	`+"for a shared memory segment exceeded available memory "`
	`428`	`+"or swap space. To reduce the request size (currently "`
	`429`	`+"%lu bytes), reduce PostgreSQL's shared memory usage, "`
	`430`	`+"perhaps by reducing shared_buffers or "`
	`431`	`+"max_connections.",`
	`432`	`+(unsigned long)AnonymousShmemSize) :0));`
`426`	`433`
`427`	`434`	`/* Now we can allocate a minimal SHM block. */`
`428`	`435`	`allocsize=sizeof(PGShmemHeader);`

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