Commit418451b

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bufmgr: Make it easier to change number of buffer state bits

In an upcoming commit I'd like to change the number of bits for the usagecount (the current max is 5, fitting in three bits, but we reserve fourbits). Until now that required adjusting a bunch of magic constants, now theconstants are defined based on the number of bits reserved.Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>Discussion:https://postgr.es/m/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6@lzx3sjsqhmt6Discussion:https://postgr.es/m/riivolmg6uzfvpzfn6wjo3ghwt42rcec43ok6mv4oenfg654y7@x7dbposbskwd

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Lines changed: 15 additions & 5 deletions

Original file line number	Diff line number	Diff line change
`@@ -39,12 +39,19 @@`
`39`	`39`	`*`
`40`	`40`	`* The definition of buffer state components is below.`
`41`	`41`	`*/`
	`42`	`+#defineBUF_REFCOUNT_BITS 18`
	`43`	`+#defineBUF_USAGECOUNT_BITS 4`
	`44`	`+#defineBUF_FLAG_BITS 10`
	`45`	`+`
	`46`	`+StaticAssertDecl(BUF_REFCOUNT_BITS+BUF_USAGECOUNT_BITS+BUF_FLAG_BITS==32,`
	`47`	`+"parts of buffer state space need to equal 32");`
	`48`	`+`
`42`	`49`	`#defineBUF_REFCOUNT_ONE 1`
`43`		`-#defineBUF_REFCOUNT_MASK ((1U <<18) - 1)`
`44`		`-#defineBUF_USAGECOUNT_MASK0x003C0000U`
`45`		`-#defineBUF_USAGECOUNT_ONE (1U <<18)`
`46`		`-#defineBUF_USAGECOUNT_SHIFT18`
`47`		`-#defineBUF_FLAG_MASK0xFFC00000U`
	`50`	`+#defineBUF_REFCOUNT_MASK ((1U <<BUF_REFCOUNT_BITS) - 1)`
	`51`	`+#defineBUF_USAGECOUNT_MASK(((1U << BUF_USAGECOUNT_BITS) - 1) << (BUF_REFCOUNT_BITS))`
	`52`	`+#defineBUF_USAGECOUNT_ONE (1U <<BUF_REFCOUNT_BITS)`
	`53`	`+#defineBUF_USAGECOUNT_SHIFTBUF_REFCOUNT_BITS`
	`54`	`+#defineBUF_FLAG_MASK(((1U << BUF_FLAG_BITS) - 1) << (BUF_REFCOUNT_BITS + BUF_USAGECOUNT_BITS))`
`48`	`55`
`49`	`56`	`/* Get refcount and usagecount from buffer state */`
`50`	`57`	`#defineBUF_STATE_GET_REFCOUNT(state) ((state) & BUF_REFCOUNT_MASK)`
`@@ -77,6 +84,9 @@`
`77`	`84`	`*/`
`78`	`85`	`#defineBM_MAX_USAGE_COUNT5`
`79`	`86`
	`87`	`+StaticAssertDecl(BM_MAX_USAGE_COUNT< (1 <<BUF_USAGECOUNT_BITS),`
	`88`	`+"BM_MAX_USAGE_COUNT doesn't fit in BUF_USAGECOUNT_BITS bits");`
	`89`	`+`
`80`	`90`	`/*`
`81`	`91`	`* Buffer tag identifies which disk block the buffer contains.`
`82`	`92`	`*`

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