diff -urNp x/drivers/ide/ide-probe.c xx/drivers/ide/ide-probe.c
--- x/drivers/ide/ide-probe.c	Mon Nov 18 06:38:10 2002
+++ xx/drivers/ide/ide-probe.c	Mon Nov 18 06:38:50 2002
@@ -814,7 +814,10 @@ static void init_gendisk (ide_hwif_t *hw
 		 * IDE can do up to 128K per request == 256
 		 */
 		*max_sect++ = ((hwif->chipset == ide_pdc4030) ? 127 : 128);
-		*max_ra++ = vm_max_readahead;
+		*max_ra = ((128*4) >> (PAGE_SHIFT - 10)) - 1; /* sequential read with 4 requests 128k large DMA */
+		if (hwif->chipset == ide_pdc4030)
+			*max_ra = ((127*4) >> (PAGE_SHIFT - 10)) - 1; /* sequential read with 4 requests 127k large DMA */
+		max_ra++;
 	}
 
 	for (unit = 0; unit < units; ++unit)
diff -urNp x/mm/filemap.c xx/mm/filemap.c
--- x/mm/filemap.c	Mon Nov 18 06:38:10 2002
+++ xx/mm/filemap.c	Mon Nov 18 06:38:50 2002
@@ -48,7 +48,7 @@ unsigned long page_cache_size;
 unsigned int page_hash_bits;
 struct page **page_hash_table;
 
-int vm_max_readahead = 31;
+int vm_max_readahead = (512 >> (PAGE_SHIFT - 10)) - 1; /* sequential read 512k large DMA */
 int vm_min_readahead = 3;
 EXPORT_SYMBOL(vm_max_readahead);
 EXPORT_SYMBOL(vm_min_readahead);