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SubjectRe: Performance of partial object-based rmap
On Fri, Feb 21, 2003 at 01:25:25AM -0300, Rik van Riel wrote:
> For object-based reverse mapping, the worst case is with large
> objects which are sparsely mapped many times (nonlinear vmas)
> and deeply inherited COW anonymous memory (apache w/ 300 children).

Actually few users of this care about time, only lowmem space. It
was (re)invented, after all, to save lowmem used for vma's.

The technical issues with 32-bit aren't anywhere near as difficult
to deal with as the massive amount of backlash anything targeted
at addressing 32-bit issues gets. These extremely irritating attempts
to marginalize every line of code written to address 32-bit issues are
probably best dealt with by showing common benefits with the so-called
"desktop" machines and/or workloads.

So witness a 768MB, 600MHz Athlon, running xmms, xterms, and mozilla:

Mem: 767376k av, 761932k used, 5444k free, 0k shrd, 70044k buff
619264k active, 104160k inactive
Swap: 506008k av, 155860k used, 350148k free 197644k cached

pte_chain 5182K 5188K 99.88%
radix_tree_node 1338K 3088K 43.32%
dentry_cache 1591K 2970K 53.59%
reiser_inode_cache 480K 1226K 39.17%
buffer_head 1040K 1043K 99.79%
size-4096 828K 828K 100.00%
size-32 796K 800K 99.54%
biovec-BIO_MAX_PAGES 768K 780K 98.46%
pgd 704K 704K 100.00%

nr_page_table_pages 689

which amounts to 2756KB RAM used for PTE's, demonstrating large
amounts of internal fragmentation within the pte_chain slab.

Reducing kernel memory consumption would reduce swapping requirements,
which generally speeds things up on the precious "desktop". The vfs
should probably get its act together too, since normal usage regularly
triggers explosive dentry_cache and reiser_inode_cache space usage.

-- wli
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