From 154cc9ea3bc840199714ee7b95277c572c5d1533 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Fri, 5 Jan 2018 17:01:37 +0000 Subject: find_ram_offset: Add comments and tracing Add some comments so I can understand the various nested loops. Add some tracing so I can see what they're doing. Signed-off-by: Dr. David Alan Gilbert Message-Id: <20180105170138.23357-2-dgilbert@redhat.com> Signed-off-by: Paolo Bonzini --- exec.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) (limited to 'exec.c') diff --git a/exec.c b/exec.c index 4722e521d4..5e2fb55080 100644 --- a/exec.c +++ b/exec.c @@ -1660,7 +1660,10 @@ static void *file_ram_alloc(RAMBlock *block, } #endif -/* Called with the ramlist lock held. */ +/* Allocate space within the ram_addr_t space that governs the + * dirty bitmaps. + * Called with the ramlist lock held. + */ static ram_addr_t find_ram_offset(ram_addr_t size) { RAMBlock *block, *next_block; @@ -1673,19 +1676,29 @@ static ram_addr_t find_ram_offset(ram_addr_t size) } RAMBLOCK_FOREACH(block) { - ram_addr_t end, next = RAM_ADDR_MAX; + ram_addr_t candidate, next = RAM_ADDR_MAX; - end = block->offset + block->max_length; + candidate = block->offset + block->max_length; + /* Search for the closest following block + * and find the gap. + */ RAMBLOCK_FOREACH(next_block) { - if (next_block->offset >= end) { + if (next_block->offset >= candidate) { next = MIN(next, next_block->offset); } } - if (next - end >= size && next - end < mingap) { - offset = end; - mingap = next - end; + + /* If it fits remember our place and remember the size + * of gap, but keep going so that we might find a smaller + * gap to fill so avoiding fragmentation. + */ + if (next - candidate >= size && next - candidate < mingap) { + offset = candidate; + mingap = next - candidate; } + + trace_find_ram_offset_loop(size, candidate, offset, next, mingap); } if (offset == RAM_ADDR_MAX) { @@ -1694,6 +1707,8 @@ static ram_addr_t find_ram_offset(ram_addr_t size) abort(); } + trace_find_ram_offset(size, offset); + return offset; } -- cgit v1.2.1