some ksm questions

[Ni zhan Chen <nizhan.chen@gmail.com>]

Hi all,

I have some detail questions about ksm. Thanks in adance. :-)

1) Why judge if(page->mapping != expected_mapping) in function get_ksm_page
called twice? And it also call put_page(page) in the second time, when this
put_page associated get_page(page) is called?

2)
in function scan_get_next_rmap_itemi 1/4 ?
if (PageAnon(*page)) ||
page_trans_compound_anon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(slot,
a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??a??
why call flush_dcache_page here? in kernel doc 
Documentation/cachetlb.txt, it
said that "Any time the kernel writes to a page cache page, _OR_ the 
kernel is
about to read from a page cache page and user space shared/writable 
mappings of
this page potentially exist, this routine is called", it is used for 
flush page
cache related cpu cache, but ksmd only scan anonymous page.

3) in function remove_rmap_item_from_tree, how to understand formula age =
(unsigned char) (ksm_scan.seqr - rmap_item->address); why need aging?

4) in function page_volatile_show, how to understand ksm_pages_volatile =
ksm_rmap_items - ksm_pages_shared - ksm_pages_sharing - 
ksm_pages_unshared; I
mean that how this formula can figure out "how many pages changing too 
fast to
be placed in a tree"?

Regards,
Chen

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