Re: [Xen-devel] [PATCH] mm: fix regression with deferred struct page init

[Juergen Gross]

On 25.06.19 10:25, Juergen Gross wrote:
> Gentle ping.
>
> I'd really like to have that in 5.2 in order to avoid the regression
> introduced with 5.2-rc1.

Adding some maintainers directly...


Juergen

> Juergen
>
> On 20.06.19 18:08, Juergen Gross wrote:
> > Commit 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time
> > instead of doing larger sections") is causing a regression on some
> > systems when the kernel is booted as Xen dom0.
> >
> > The system will just hang in early boot.
> >
> > Reason is an endless loop in get_page_from_freelist() in case the first
> > zone looked at has no free memory. deferred_grow_zone() is always
> > returning true due to the following code snipplet:
> >
> > ÂÂ /* If the zone is empty somebody else may have cleared out the zone */
> > ÂÂ if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ first_deferred_pfn)) {
> > ÂÂÂÂÂÂÂÂÂÂ pgdat->first_deferred_pfn = ULONG_MAX;
> > ÂÂÂÂÂÂÂÂÂÂ pgdat_resize_unlock(pgdat, &flags);
> > ÂÂÂÂÂÂÂÂÂÂ return true;
> > ÂÂ }
> >
> > This in turn results in the loop as get_page_from_freelist() is
> > assuming forward progress can be made by doing some more struct page
> > initialization.
> >
> > Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time 
> > instead of doing larger sections")
> > Suggested-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > Â mm/page_alloc.c | 3 ++-
> > Â 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d66bc8abe0af..8e3bc949ebcc 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1826,7 +1826,8 @@ deferred_grow_zone(struct zone *zone, unsigned 
> > int order)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ first_deferred_pfn)) {
> > ÂÂÂÂÂÂÂÂÂ pgdat->first_deferred_pfn = ULONG_MAX;
> > ÂÂÂÂÂÂÂÂÂ pgdat_resize_unlock(pgdat, &flags);
> > -ÂÂÂÂÂÂÂ return true;
> > +ÂÂÂÂÂÂÂ /* Retry only once. */
> > +ÂÂÂÂÂÂÂ return first_deferred_pfn != ULONG_MAX;
> > ÂÂÂÂÂ }
> > ÂÂÂÂÂ /*
>
>
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