On Thu, Apr 01, 2021 at 11:17:37AM -0700, Suren Baghdasaryan wrote: > From: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> > > Add an optimization for KSM pages almost in the same way that we have > for ordinary anonymous pages. If there is a write fault in a page, > which is mapped to an only pte, and it is not related to swap cache; the > page may be reused without copying its content. > > [ Note that we do not consider PageSwapCache() pages at least for now, > since we don't want to complicate __get_ksm_page(), which has nice > optimization based on this (for the migration case). Currenly it is > spinning on PageSwapCache() pages, waiting for when they have > unfreezed counters (i.e., for the migration finish). But we don't want > to make it also spinning on swap cache pages, which we try to reuse, > since there is not a very high probability to reuse them. So, for now > we do not consider PageSwapCache() pages at all. ] > > So in reuse_ksm_page() we check for 1) PageSwapCache() and 2) > page_stable_node(), to skip a page, which KSM is currently trying to > link to stable tree. Then we do page_ref_freeze() to prohibit KSM to > merge one more page into the page, we are reusing. After that, nobody > can refer to the reusing page: KSM skips !PageSwapCache() pages with > zero refcount; and the protection against of all other participants is > the same as for reused ordinary anon pages pte lock, page lock and > mmap_sem. > > [akpm@xxxxxxxxxxxxxxxxxxxx: replace BUG_ON()s with WARN_ON()s] > Link: http://lkml.kernel.org/r/154471491016.31352.1168978849911555609.stgit@localhost.localdomain > Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> > Reviewed-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Cc: Christian Koenig <christian.koenig@xxxxxxx> > Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxxx> > Cc: Huang Ying <ying.huang@xxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > --- > include/linux/ksm.h | 7 +++++++ > mm/ksm.c | 30 ++++++++++++++++++++++++++++-- > mm/memory.c | 16 ++++++++++++++-- > 3 files changed, 49 insertions(+), 4 deletions(-) You forgot to put the git commit id of the upstream commit in here somewhere so we can properly reference it and track it. When/if you resend this, please add it to all of the commits. thanks, greg k-h
