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Re: [RFA/dwarf] Allocate abbrevs from a new obstack
- From: Jim Blandy <jimb at redhat dot com>
- To: Daniel Jacobowitz <drow at false dot org>
- Cc: gdb-patches at sources dot redhat dot com, Elena Zannoni <ezannoni at redhat dot com>
- Date: 26 Feb 2004 17:09:36 -0500
- Subject: Re: [RFA/dwarf] Allocate abbrevs from a new obstack
- References: <20040225035543.GA13672@nevyn.them.org>
Daniel Jacobowitz <drow@false.org> writes:
> Another independent performance optimization from my profiling. This one is
> good for several percent speedup on mainline. My original description:
>
> - It plugs a huge memory leak. After loading partial symbols for
> libc, GDB uses 5.6MB memory without this patch and 1.6MB with it.
> We weren't emptying the abbrev table.
>
> [Specifically, we were emptying it after dwarf2_build_psymtabs_hard,
> instead of once each time through the loop. dwarf2_read_abbrevs then
> zeroed out the allocated, unreferenced pointers.]
>
> - I spent a lot of time trying to find alternate data structures that
> would be more efficient. The expandable hash table is slower, even if
> you initially allocate it to the right size. The splay tree I expected
> to be quite good in this case, but it isn't either; the overhead is simply
> too high. The fixed-size ad-hoc hash table appears to be the best we can
> do.
>
> Tested on i686-pc-linux-gnu, no regressions. OK to commit?
Looks great --- please do.