Re: Help Needed

[Kaustubh Atrawalkar <kaustubh atrawalkar celunite com>]

Federico Mena Quintero wrote:
> 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
Yes we have *really* tight constraints. One more thing about the slab 
allocator. As per my study the slab allocator uses POSIX_MEMALIGN to 
allocate blocks of memory at a time though only small amount of that is 
used at that time. This chunk size can be set and can be disabled 
through G_SLICE environment variable. My requirement of memory is at the 
most 2Mb (means the apps wont exceed this limit) then can removing the 
slab allocator will help me ? I can see the noticeable change in small 
apps (less than aroung 300/400k) but not in large apps. Comment plz.