Re: Help Needed

[Federico Mena Quintero <federico ximian com>]

On Wed, 2006-08-16 at 15:39 +0530, Kaustubh Atrawalkar wrote:

> I am working on glib optimization for our product. I just need to know 
> what is the use of G_QUARK_BLOCK_SIZE (defined in gdataset.c) and used 
> while allocating memory for any types? Also why we need the size 512 
> bytes for that quark block? Cant we reduce them to say 64 bytes or 
> somewhat like that. We have very critical memory requirement. So need so 
> save as much memory as possible. If you can give me some more hot spots 
> where i can save more memory it will be very helpful to me.

Quarks are stored as an array which maps quark IDs to strings, and in a
hash table which maps strings to quark IDs.

When you register a new quark, you may need to grow the array of quark
IDs.  G_QUARK_BLOCK_SIZE is simply the number of quarks that can be
registered before the array needs to be re-grown.  This is the code from
the internal g_quark_new():

  if (g_quark_seq_id % G_QUARK_BLOCK_SIZE == 0)
    g_quarks = g_renew (gchar*, g_quarks, g_quark_seq_id + G_QUARK_BLOCK_SIZE);
  ...
  quark = g_quark_seq_id++;
  g_quarks[quark] = string;
  g_hash_table_insert (g_quark_ht, string, GUINT_TO_POINTER (quark));

You can certainly make that number smaller.  Remember that on average
half of G_QUARK_BLOCK_SIZE will be "wasted space" from the unused
entries at the end of the array.  On a 32-bit machine, this would be 
512 * sizeof (gpointer) / 2 = just 1 KB per process.  That's probably
too small a value to optimize for, unless you have *really* tight
constraints.

  Federico