Simplify coding in slru.c

New code in 53c2a97a9266 uses direct array access to
shared->bank_locks[bankno].lock which can be made a little bit more
legible by using the SimpleLruGetBankLock helper function.
Nothing terribly serious, but let's add some clarity.

Discussion: https://postgr.es/m/202403041517.3a35jw53os65@alvherre.pgsql

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index f774d285b7fe42a6ea4d53412b8bb49708990f8b..6895266bf9dff9bcf2f3510dda58a822cb90eff0 100644 (file)
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -489,14 +489,14 @@ SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
                                  TransactionId xid)
 {
        SlruShared      shared = ctl->shared;
+       LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
 
-       Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
+       Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
 
        /* Outer loop handles restart if we must wait for someone else's I/O */
        for (;;)
        {
                int                     slotno;
-               int                     bankno;
                bool            ok;
 
                /* See if page already is in memory; if not, pick victim slot */
@@ -539,10 +539,9 @@ SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
 
                /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
                LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
-               bankno = SlotGetBankNumber(slotno);
 
                /* Release bank lock while doing I/O */
-               LWLockRelease(&shared->bank_locks[bankno].lock);
+               LWLockRelease(banklock);
 
                /* Do the read */
                ok = SlruPhysicalReadPage(ctl, pageno, slotno);
@@ -551,7 +550,7 @@ SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
                SimpleLruZeroLSNs(ctl, slotno);
 
                /* Re-acquire bank control lock and update page state */
-               LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
+               LWLockAcquire(banklock, LW_EXCLUSIVE);
 
                Assert(shared->page_number[slotno] == pageno &&
                           shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
@@ -592,12 +591,13 @@ int
 SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
 {
        SlruShared      shared = ctl->shared;
+       LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
        int                     bankno = pageno & ctl->bank_mask;
        int                     bankstart = bankno * SLRU_BANK_SIZE;
        int                     bankend = bankstart + SLRU_BANK_SIZE;
 
        /* Try to find the page while holding only shared lock */
-       LWLockAcquire(&shared->bank_locks[bankno].lock, LW_SHARED);
+       LWLockAcquire(banklock, LW_SHARED);
 
        /* See if page is already in a buffer */
        for (int slotno = bankstart; slotno < bankend; slotno++)
@@ -617,8 +617,8 @@ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
        }
 
        /* No luck, so switch to normal exclusive lock and do regular read */
-       LWLockRelease(&shared->bank_locks[bankno].lock);
-       LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
+       LWLockRelease(banklock);
+       LWLockAcquire(banklock, LW_EXCLUSIVE);
 
        return SimpleLruReadPage(ctl, pageno, true, xid);
 }
@@ -1167,7 +1167,7 @@ SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
                int                     bankstart = bankno * SLRU_BANK_SIZE;
                int                     bankend = bankstart + SLRU_BANK_SIZE;
 
-               Assert(LWLockHeldByMe(&shared->bank_locks[bankno].lock));
+               Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
 
                /* See if page already has a buffer assigned */
                for (int slotno = 0; slotno < shared->num_slots; slotno++)