Re: [PATCH 2/5] cpuset memory spread page cache implementation and hooks

[Paul Jackson <pj@sgi.com>]

Earlier Andrew wrote:
> Really has two forms, depending upon Kconfig.
> 
> 1:
> 
> static inline struct page *page_cache_alloc(struct address_space *x)
> {
> 	return alloc_pages(mapping_gfp_mask(x), 0);
> }
> 
> That should be inlined.
> 
> 2:
> 
> static inline struct page *page_cache_alloc(struct address_space *x)
> {
> 	if (cpuset_mem_spread_check()) {
> 		int n = cpuset_mem_spread_node();
> 		return alloc_pages_node(n, mapping_gfp_mask(x), 0);
> 	}
> 	return alloc_pages(mapping_gfp_mask(x), 0);
> }

Later on, he wrote:
> I'm saying "gee, that looks big.  Do you have time to investigate possible
> improvements?"   They may come to naught.

After playing around with the variations we've considered on this
thread, the results are simple enough.  I experimented with just
the 3 calls to page_cache_alloc_cold() in mm/filemap.c, because that
was easy, and all these calls have the same shape.

    For non-NUMA, removing 'inline' from the three page_cache_alloc_cold()
    calls in mm/filemap.c would cost a total of 16 bytes text size

    For NUMA+CPUSET, removing it would _save_ 583 bytes total over the
    three calls.

    The "nm -S" size of the uninlined page_cache_alloc_cold() is 448 bytes
    (it was 96 bytes before this cpuset patchset).

    This is all on ia64 sn2_defconfig gcc 3.3.3.

The conclusion is straight forward, and as Andrew suspected.

We want these two page_cache_alloc*() routines out of line in the
NUMA case, but left inline for the non-NUMA case.

I will follow up with a simple patch that makes it easy to mark
routines that should be inline for UMA, out of line for NUMA.

These two page_cache_alloc*(), and perhaps also __cache_alloc() when
Pekka or I gets a handle on it, are candidates for this marking, as
routines to inline on UMA, out of line on NUMA.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401
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