Performance / Memory Usage Patch

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It gives (hopefully) linux-2.1.32 a _small_ performance boost, and a reduction in memory usage. It is not rocket-science.

The patch contains;

• The latest version (almost) of the SLAB allocator. This new version supports head-&-tail red-zoning, object poisioning, and stat collecting, along with better management of large objects (the hash-table has gone).
• kmalloc()/kfree() are now built on top of the SLAB.
• Several allocations now use the SLAB directly, either by having there own obj-cache, or by obtaining a ptr to one of the general-size caches (kmem_find_general_cachep()).
• Alignment of some structures to be L1 cache friendly.
• Removal of the swap_cache array (which always caused a 'far' memory reference in free_page()). The test now uses the flag member in 'struct page' and pg_swap_entry.
• Removal of tests against mem_map[].count in fs/buffer.c Buffer pages can only ever have a count of 1 (at least I think so....).
• Removal of the test for a buffer page in filemap_write_page(). As far as I can tell, there is no-way for buffer pages to be mapped into a task's address space (not even via /dev/kmem, which only maps Reserved pages).
• Reduction in size of "struct page". A page cannot be both in the buffer-cache and named-page-cache at the same time, neither can it be in either of these caches and be an anonymous page (which means it can be marked swap-cached). NOTE: the "pg_map_nr" is now only valid for a free page. This is only temporary, to make the structure have an even number of members (so common members can be paired to make them L1 friendly).
• If my maths are correct, the memory that was being reserved for the buddy maps (page_alloc.c) was twice the amount necessary.
• A few functions (in filemap.c and do_wp_page()) now hang-on to a page (via global cache_page variables) to prevent them from thrashing the gfp() functions.
• Slightly optimised versions of clear_page() and copy_page(). I'm no ASM programmer, and these are just in there to see what happens (certain helps on my 486 test target).
• Remove a race in fs/inode.c, and reduce the amount of zeroing of inodes. Also improves the partial ordering of the inode freelist.
• Few changes in mm/swapfile.c to use ptrs rather than indices.
• A new page allocation function for allocating single pages for priority GFP_USER (the priority at which all user pages should be allocated).

I'd appreciate anyone giving this patch a trying, but a few points to note:

The figures under "lmbench" show limited/no improvement, but running other tests (such as a large number of kernel compiles) do show a performance increase (particularly on a 486 box).

I believe networking throughput/latencies take a small performance hit. This is probably due to different byte alignments of dynamically allocated memory. I do not understand the networking code - perhaps somebody could try SLABising it (making sure common accessed members are on the same h/w cache line, and using kmem_find_general_cachep()).

The second argument to kfree_s() is now honoured rather than being thrown away by the pre-processor. This did cause compile problems for ipv4 (fixes in the patch).