Revert "Tune zio buffer caches and their alignments"

This reverts commit bd7a02c which
can trigger an unlikely existing bio alignment issue on Linux.
This change is good, but the underlying issue it exposes needs to
be resolved before this can be re-applied.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue openzfs#15533
Issue openzfs#16631

module/zfs/zio.c

@@ -159,22 +159,23 @@ zio_init(void)
 	zio_link_cache = kmem_cache_create("zio_link_cache",
 	    sizeof (zio_link_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
 
+	/*
+	 * For small buffers, we want a cache for each multiple of
+	 * SPA_MINBLOCKSIZE.  For larger buffers, we want a cache
+	 * for each quarter-power of 2.
+	 */
 	for (c = 0; c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; c++) {
 		size_t size = (c + 1) << SPA_MINBLOCKSHIFT;
-		size_t align, cflags, data_cflags;
-		char name[32];
-
-		/*
-		 * Create cache for each half-power of 2 size, starting from
-		 * SPA_MINBLOCKSIZE.  It should give us memory space efficiency
-		 * of ~7/8, sufficient for transient allocations mostly using
-		 * these caches.
-		 */
 		size_t p2 = size;
+		size_t align = 0;
+		size_t data_cflags, cflags;
+
+		data_cflags = KMC_NODEBUG;
+		cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ?
+		    KMC_NODEBUG : 0;
+
 		while (!ISP2(p2))
 			p2 &= p2 - 1;
-		if (!IS_P2ALIGNED(size, p2 / 2))
-			continue;
 
 #ifndef _KERNEL
 		/*
@@ -185,41 +186,47 @@ zio_init(void)
 		 */
 		if (arc_watch && !IS_P2ALIGNED(size, PAGESIZE))
 			continue;
-#endif
-
-		if (IS_P2ALIGNED(size, PAGESIZE))
+		/*
+		 * Here's the problem - on 4K native devices in userland on
+		 * Linux using O_DIRECT, buffers must be 4K aligned or I/O
+		 * will fail with EINVAL, causing zdb (and others) to coredump.
+		 * Since userland probably doesn't need optimized buffer caches,
+		 * we just force 4K alignment on everything.
+		 */
+		align = 8 * SPA_MINBLOCKSIZE;
+#else
+		if (size < PAGESIZE) {
+			align = SPA_MINBLOCKSIZE;
+		} else if (IS_P2ALIGNED(size, p2 >> 2)) {
 			align = PAGESIZE;
-		else
-			align = 1 << (highbit64(size ^ (size - 1)) - 1);
-
-		cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ?
-		    KMC_NODEBUG : 0;
-		data_cflags = KMC_NODEBUG;
-		if (abd_size_alloc_linear(size)) {
-			cflags |= KMC_RECLAIMABLE;
-			data_cflags |= KMC_RECLAIMABLE;
 		}
-		if (cflags == data_cflags) {
-			/*
-			 * Resulting kmem caches would be identical.
-			 * Save memory by creating only one.
-			 */
-			(void) snprintf(name, sizeof (name),
-			    "zio_buf_comb_%lu", (ulong_t)size);
-			zio_buf_cache[c] = kmem_cache_create(name, size, align,
-			    NULL, NULL, NULL, NULL, NULL, cflags);
-			zio_data_buf_cache[c] = zio_buf_cache[c];
-			continue;
+#endif
+
+		if (align != 0) {
+			char name[36];
+			if (cflags == data_cflags) {
+				/*
+				 * Resulting kmem caches would be identical.
+				 * Save memory by creating only one.
+				 */
+				(void) snprintf(name, sizeof (name),
+				    "zio_buf_comb_%lu", (ulong_t)size);
+				zio_buf_cache[c] = kmem_cache_create(name,
+				    size, align, NULL, NULL, NULL, NULL, NULL,
+				    cflags);
+				zio_data_buf_cache[c] = zio_buf_cache[c];
+				continue;
+			}
+			(void) snprintf(name, sizeof (name), "zio_buf_%lu",
+			    (ulong_t)size);
+			zio_buf_cache[c] = kmem_cache_create(name, size,
+			    align, NULL, NULL, NULL, NULL, NULL, cflags);
+
+			(void) snprintf(name, sizeof (name), "zio_data_buf_%lu",
+			    (ulong_t)size);
+			zio_data_buf_cache[c] = kmem_cache_create(name, size,
+			    align, NULL, NULL, NULL, NULL, NULL, data_cflags);
 		}
-		(void) snprintf(name, sizeof (name), "zio_buf_%lu",
-		    (ulong_t)size);
-		zio_buf_cache[c] = kmem_cache_create(name, size, align,
-		    NULL, NULL, NULL, NULL, NULL, cflags);
-
-		(void) snprintf(name, sizeof (name), "zio_data_buf_%lu",
-		    (ulong_t)size);
-		zio_data_buf_cache[c] = kmem_cache_create(name, size, align,
-		    NULL, NULL, NULL, NULL, NULL, data_cflags);
 	}
 
 	while (--c != 0) {