On Wed, Sep 07, 2022 at 04:34:11PM -0700, Andrew Morton wrote: > > The patch titled > Subject: mm: avoid unnecessary page table walk for __get_user_pages > has been added to the -mm mm-unstable branch. Its filename is > mm-avoid-unnecessary-page-table-walk-for-__get_user_pages.patch > > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-avoid-unnecessary-page-table-walk-for-__get_user_pages.patch > > This patch will later appear in the mm-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Chen Wandun <chenwandun@xxxxxxxxxx> > Subject: mm: avoid unnecessary page table walk for __get_user_pages > Date: Tue, 6 Sep 2022 10:44:01 +0800 > > There is no need to walk page tables and find pages if faultin_page)_ > succeeds and __get_user_pages)_ doesn't care about populating the pages[] > array. So directly go on to handle the next page. > > Link: https://lkml.kernel.org/r/20220906024401.133336-1-chenwandun@xxxxxxxxxx > Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> > Cc: John Hubbard <jhubbard@xxxxxxxxxx> > Cc: Peter Xu <peterx@xxxxxxxxxx> > Cc: Alistair Popple <apopple@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > mm/gup.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > --- a/mm/gup.c~mm-avoid-unnecessary-page-table-walk-for-__get_user_pages > +++ a/mm/gup.c > @@ -1175,7 +1175,10 @@ retry: > PTR_ERR(page) == -EMLINK, locked); > switch (ret) { > case 0: > - goto retry; > + if (pages) > + goto retry; > + else > + goto next_page; > case -EBUSY: > case -EAGAIN: > ret = 0; Will this mess up the refcounts already? afaict follow_page_mask() is the only place to grab the pages, and GUP should need to take refcounts on pages even without pages** being passed in. Meanwhile I'd think there will be cases that require multiple entrances of continuous follow_page_mask() + faultin_page() sequences, that even the previous round of faultin_page() returned success but follow_page_mask() may still want one more round of faulting for some reason to finally grab the correct page. > _ > > Patches currently in -mm which might be from chenwandun@xxxxxxxxxx are > > mm-avoid-unnecessary-page-table-walk-for-__get_user_pages.patch > -- Peter Xu
