On Tue 26-10-21 21:33:15, Uladzislau Rezki wrote:
> On Tue, Oct 26, 2021 at 06:28:52PM +0200, Michal Hocko wrote:
> > On Tue 26-10-21 17:48:32, Uladzislau Rezki wrote:
> > > > From: Michal Hocko <mhocko@xxxxxxxx>
> > > >
> > > > Dave Chinner has mentioned that some of the xfs code would benefit from
> > > > kvmalloc support for __GFP_NOFAIL because they have allocations that
> > > > cannot fail and they do not fit into a single page.
> > > >
> > > > The larg part of the vmalloc implementation already complies with the
> > > > given gfp flags so there is no work for those to be done. The area
> > > > and page table allocations are an exception to that. Implement a retry
> > > > loop for those.
> > > >
> > > > Add a short sleep before retrying. 1 jiffy is a completely random
> > > > timeout. Ideally the retry would wait for an explicit event - e.g.
> > > > a change to the vmalloc space change if the failure was caused by
> > > > the space fragmentation or depletion. But there are multiple different
> > > > reasons to retry and this could become much more complex. Keep the retry
> > > > simple for now and just sleep to prevent from hogging CPUs.
> > > >
> > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> > > > ---
> > > > mm/vmalloc.c | 10 +++++++++-
> > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index c6cc77d2f366..602649919a9d 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -2941,8 +2941,12 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> > > > else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
> > > > flags = memalloc_noio_save();
> > > >
> > > > - ret = vmap_pages_range(addr, addr + size, prot, area->pages,
> > > > + do {
> > > > + ret = vmap_pages_range(addr, addr + size, prot, area->pages,
> > > > page_shift);
> > > > + if (ret < 0)
> > > > + schedule_timeout_uninterruptible(1);
> > > > + } while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
> > > >
> > >
> > > 1.
> > > After that change a below code:
> > >
> > > <snip>
> > > if (ret < 0) {
> > > warn_alloc(orig_gfp_mask, NULL,
> > > "vmalloc error: size %lu, failed to map pages",
> > > area->nr_pages * PAGE_SIZE);
> > > goto fail;
> > > }
> > > <snip>
> > >
> > > does not make any sense anymore.
> >
> > Why? Allocations without __GFP_NOFAIL can still fail, no?
> >
> Right. I meant one thing but wrote slightly differently. In case of
> vmap_pages_range() fails(if __GFP_NOFAIL is set) should we emit any
> warning message? Because either we can recover on a future iteration
> or it stuck there infinitely so a user does not understand what happened.
> From the other hand this is how __GFP_NOFAIL works, hm..
Yes, the page allocator doesn't warn either and I would like to keep
this in sync.
> Another thing, i see that schedule_timeout_uninterruptible(1) is invoked
> for all cases even when __GFP_NOFAIL is not set, in that scenario we do
> not want to wait, instead we should return back to a caller asap. Or am
> i missing something here?
OK, I will change that.
--
Michal Hocko
SUSE Labs
