From 716e11a592fd7df6a7e263d9b6237ff96d98c4db Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Fri, 21 Feb 2025 13:08:11 -0500 Subject: [PATCH v2 3/4] 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 usage count (the current max is 5, fitting in three bits, but we reserve four bits). Until now that required adjusting a bunch of magic constants, now the constants are defined based on the number of bits reserved. Reviewed-by: Heikki Linnakangas Discussion: https://postgr.es/m/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6@lzx3sjsqhmt6 --- src/include/storage/buf_internals.h | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h index 1a65342177d..d830d5c9841 100644 --- a/src/include/storage/buf_internals.h +++ b/src/include/storage/buf_internals.h @@ -39,12 +39,19 @@ * * The definition of buffer state components is below. */ +#define BUF_REFCOUNT_BITS 18 +#define BUF_USAGECOUNT_BITS 4 +#define BUF_FLAG_BITS 10 + +StaticAssertDecl(BUF_REFCOUNT_BITS + BUF_USAGECOUNT_BITS + BUF_FLAG_BITS == 32, + "parts of buffer state space need to equal 32"); + #define BUF_REFCOUNT_ONE 1 -#define BUF_REFCOUNT_MASK ((1U << 18) - 1) -#define BUF_USAGECOUNT_MASK 0x003C0000U -#define BUF_USAGECOUNT_ONE (1U << 18) -#define BUF_USAGECOUNT_SHIFT 18 -#define BUF_FLAG_MASK 0xFFC00000U +#define BUF_REFCOUNT_MASK ((1U << BUF_REFCOUNT_BITS) - 1) +#define BUF_USAGECOUNT_MASK (((1U << BUF_USAGECOUNT_BITS) - 1) << (BUF_REFCOUNT_BITS)) +#define BUF_USAGECOUNT_ONE (1U << BUF_REFCOUNT_BITS) +#define BUF_USAGECOUNT_SHIFT BUF_REFCOUNT_BITS +#define BUF_FLAG_MASK (((1U << BUF_FLAG_BITS) - 1) << (BUF_REFCOUNT_BITS + BUF_USAGECOUNT_BITS)) /* Get refcount and usagecount from buffer state */ #define BUF_STATE_GET_REFCOUNT(state) ((state) & BUF_REFCOUNT_MASK) @@ -77,6 +84,9 @@ */ #define BM_MAX_USAGE_COUNT 5 +StaticAssertDecl(BM_MAX_USAGE_COUNT < (1 << BUF_USAGECOUNT_BITS), + "BM_MAX_USAGE_COUNT doesn't fit in BUF_USAGECOUNT_BITS bits"); + /* * Buffer tag identifies which disk block the buffer contains. * -- 2.48.1.76.g4e746b1a31.dirty