On Thu, Apr 1, 2021 at 12:38 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > 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. Will do. Thanks! > > thanks, > > greg k-h
