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List: linux-ext4
Subject: Re: Need to potentially watch stack usage for ext4 and AIO...
From: Eric Sandeen <sandeen () redhat ! com>
Date: 2009-06-25 4:58:46
Message-ID: 4A430406.2080904 () redhat ! com
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Eric Sandeen wrote:
> I had found some tools once to do static callchain analysis & graph
> them, maybe time to break it out again.
codeviz was the tool; getting it to work is fiddly. But here, for
example, are some of the callers of ext4_mb_init_cache() (one of the
functions at the bottom of your deep chain), with stack usage and
piggish ones highlighted in red:
http://sandeen.fedorapeople.org/ext4/ext4_mb_init_cache_callers.png
This is actually only analysis of the functions in mballoc.c, but that's
relevant for the static / noinline decisions.
The stack usage values were after my attempt to get gcc to inline
-nothing- at all.
So there you can see that ext4_mb_regular_allocator by itself uses 104
bytes, but calls several other functions which get inlined normally:
ext4_mb_try_best_found 16
ext4_mb_try_by_goal 56
ext4_mb_load_buddy 24
ext4_mb_init_group 24
Without all the noinlining, ext4_mb_regular_allocator uses 232 bytes ...
104+16+56+24+24 = 224 is close to that.
On the flip side here are the functions called by
ext4_mb_init_cache_callees within mballoc.c:
http://sandeen.fedorapeople.org/ext4/ext4_mb_init_cache_callees.png
Here too I think you can see that if much of that gets inlined, it'll
bloat that function.
A bit more analysis like this might yield some prudent changes ... but
it's tedious. :)
-Eric
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