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diff --git a/Documentation/vm/uksm.txt b/Documentation/vm/uksm.txt new file mode 100644 index 000000000..387d96ae2 --- /dev/null +++ b/Documentation/vm/uksm.txt @@ -0,0 +1,59 @@ +The Ultra Kernel Samepage Merging feature +---------------------------------------------- +/* + * Ultra KSM. Copyright (C) 2011-2012 Nai Xia + * + * This is an improvement upon KSM. Some basic data structures and routines + * are borrowed from ksm.c . + * + * Its new features: + * 1. Full system scan: + * It automatically scans all user processes' anonymous VMAs. Kernel-user + * interaction to submit a memory area to KSM is no longer needed. + * + * 2. Rich area detection: + * It automatically detects rich areas containing abundant duplicated + * pages based. Rich areas are given a full scan speed. Poor areas are + * sampled at a reasonable speed with very low CPU consumption. + * + * 3. Ultra Per-page scan speed improvement: + * A new hash algorithm is proposed. As a result, on a machine with + * Core(TM)2 Quad Q9300 CPU in 32-bit mode and 800MHZ DDR2 main memory, it + * can scan memory areas that does not contain duplicated pages at speed of + * 627MB/sec ~ 2445MB/sec and can merge duplicated areas at speed of + * 477MB/sec ~ 923MB/sec. + * + * 4. Thrashing area avoidance: + * Thrashing area(an VMA that has frequent Ksm page break-out) can be + * filtered out. My benchmark shows it's more efficient than KSM's per-page + * hash value based volatile page detection. + * + * + * 5. Misc changes upon KSM: + * * It has a fully x86-opitmized memcmp dedicated for 4-byte-aligned page + * comparison. It's much faster than default C version on x86. + * * rmap_item now has an struct *page member to loosely cache a + * address-->page mapping, which reduces too much time-costly + * follow_page(). + * * The VMA creation/exit procedures are hooked to let the Ultra KSM know. + * * try_to_merge_two_pages() now can revert a pte if it fails. No break_ + * ksm is needed for this case. + * + * 6. Full Zero Page consideration(contributed by Figo Zhang) + * Now uksmd consider full zero pages as special pages and merge them to an + * special unswappable uksm zero page. + */ + +ChangeLog: + +2012-05-05 The creation of this Doc +2012-05-08 UKSM 0.1.1.1 libc crash bug fix, api clean up, doc clean up. +2012-05-28 UKSM 0.1.1.2 bug fix release +2012-06-26 UKSM 0.1.2-beta1 first beta release for 0.1.2 +2012-07-2 UKSM 0.1.2-beta2 +2012-07-10 UKSM 0.1.2-beta3 +2012-07-26 UKSM 0.1.2 Fine grained speed control, more scan optimization. +2012-10-13 UKSM 0.1.2.1 Bug fixes. +2012-12-31 UKSM 0.1.2.2 Minor bug fixes. +2014-07-02 UKSM 0.1.2.3 Fix a " __this_cpu_read() in preemptible bug". +2015-04-22 UKSM 0.1.2.4 Fix a race condition that can sometimes trigger anonying warnings. |