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Re: [PATCH] LTO streamer reorg - try to reduce WPA memory use


On 2014.07.29 at 15:10 +0200, Richard Biener wrote:
> On Tue, 29 Jul 2014, Richard Biener wrote:
> 
> > 
> > This re-organizes the LTO streamer to do compression transparently
> > in the data-streamer routines (and disables section compression
> > by defaulting to -flto-compression-level=0).  This avoids
> > keeping the whole uncompressed sections in memory, only retaining
> > the compressed ones.
> > 
> > The downside is that we lose compression of at least the string
> > parts (they are abusing the streaming interface quite awkwardly
> > and doing random-accesses with offsets into the uncompressed
> > section).  With a little bit of surgery we can get that back I
> > think (but we'd have to keep the uncompressed piece in memory
> > somewhere which means losing the memory use advantage).
> > 
> > Very lightly tested sofar (running lto.exp).  I'll try a LTO
> > bootstrap now.
> > 
> > I wonder what the change is on WPA memory use for larger
> > projects and what the effect on object file size is.
> 
> Updated patch passing LTO bootstrap (one warning fix) and
> with a memory leak fixed.

Testing with Firefox is impossible at the moment because of PR61885.
One thing I've noticed (before the ICE) is that virtual memory usage is
very high:

Address            Kbytes      RSS    Dirty  Mode  Mapping
0000000000400000    16344     9084        0  r-x-- lto1
00000000013f6000       36       36       28  rw--- lto1
00000000013ff000     1072      276      276  rw---   [ anon ]
00000000034aa000 10154940  1540384  1540384  rw---   [ anon ]
00002acf04af2000      136      136        0  r-x-- ld-2.19.90.so
00002acf04b14000       88       88       88  rw---   [ anon ]
...
----------------  -------  -------  ------- 
total kB         12022060  3388396  3377708

-- 
Markus


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