Optimize execution time of the memdump tool

tools/android/memdump/memdump.cc

Index: tools/android/memdump/memdump.cc
diff --git a/tools/android/memdump/memdump.cc b/tools/android/memdump/memdump.cc
index 50a5914e1e76b9df99f08bb17a5c6f4b640e65f3..9545c0dbee8014d591f4d18dddee69d2ae79b5a0 100644
--- a/tools/android/memdump/memdump.cc
+++ b/tools/android/memdump/memdump.cc
@@ -200,15 +200,23 @@ bool GetPagesForMemoryMap(int pagemap_fd,
                           const MemoryMap& memory_map,
                           std::vector<PageInfo>* committed_pages,
                           BitSet* committed_pages_bits) {
+  off64_t offset = memory_map.start_address / kPageSize;

[Philippe, 2014/02/26 12:05:48]

Nit: const off64_t offset

Reviewers in Chromium would not make this comment usually, but you will notice
here that we use constness extensively :) (mostly for documentation
purpose/extra type safety).

[hyunki, 2014/02/27 01:15:06]

Done.

+  if (lseek64(pagemap_fd, offset * sizeof(PageMapEntry), SEEK_SET) < 0) {
+    PLOG(ERROR) << "lseek";
+    return false;
+  }
   for (uint addr = memory_map.start_address, page_index = 0;
        addr < memory_map.end_address;
        addr += kPageSize, ++page_index) {
     DCHECK_EQ(0, addr % kPageSize);
     PageMapEntry page_map_entry = {};
     COMPILE_ASSERT(sizeof(PageMapEntry) == sizeof(uint64), unexpected_size);
-    const off64_t offset = addr / kPageSize;
-    if (!ReadFromFileAtOffset(pagemap_fd, offset, &page_map_entry))
+    offset++;

[Philippe, 2014/02/26 12:05:48]

Nit: You don't seem to be using |offset| in the loop so you can drop this line
(which also allows |offset| to be const).

[hyunki, 2014/02/27 01:15:06]

Done.

+    ssize_t bytes = read(pagemap_fd, &page_map_entry, sizeof(PageMapEntry));

[Philippe, 2014/02/26 12:05:48]

Nit: sizeof(page_map_entry) would be slightly better. And to add an extra const,
you can rewrite this line like this (if it doesn't fit on a single line):

const ssize_t bytes = read(
    pagemap_fd, &page_map_entry, sizeof(page_map_entry));

[hyunki, 2014/02/27 01:15:06]

Done.

+    if (bytes != sizeof(PageMapEntry) && bytes != 0) {
+      PLOG(ERROR) << "read";
       return false;
+    }
     if (page_map_entry.present) {  // Ignore non-committed pages.
       if (page_map_entry.page_frame_number == 0)
         continue;