On Wed 23-07-14 15:50:09, David Rientjes wrote: > The page allocator relies on __GFP_WAIT to determine if ALLOC_CPUSET > should be set in allocflags. ALLOC_CPUSET controls if a page allocation > should be restricted only to the set of allowed cpuset mems. > > Transparent hugepages clears __GFP_WAIT when defrag is disabled to prevent > the fault path from using memory compaction or direct reclaim. Thus, it > is unfairly able to allocate outside of its cpuset mems restriction as a > side-effect. > > This patch ensures that ALLOC_CPUSET is only cleared when the gfp mask is > truly GFP_ATOMIC by verifying it is also not a thp allocation. > > Reported-by: Alex Thorlton <[email protected]> > Cc: [email protected] > Signed-off-by: David Rientjes <[email protected]>
This is an abuse of __GFP_NO_KSWAPD but it also looks like a new gfp flag would need to be added to do it in other way. No other users seem to clear GFP_WAIT while using __GFP_NO_KSWAPD AFAICS so this should really affect only THP allocations. Reviewed-by: Michal Hocko <[email protected]> > --- > mm/page_alloc.c | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2447,7 +2447,7 @@ static inline int > gfp_to_alloc_flags(gfp_t gfp_mask) > { > int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET; > - const gfp_t wait = gfp_mask & __GFP_WAIT; > + const bool atomic = !(gfp_mask & (__GFP_WAIT | __GFP_NO_KSWAPD)); > > /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. > */ > BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH); > @@ -2456,20 +2456,20 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > * The caller may dip into page reserves a bit more if the caller > * cannot run direct reclaim, or if the caller has realtime scheduling > * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will > - * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH). > + * set both ALLOC_HARDER (atomic == true) and ALLOC_HIGH (__GFP_HIGH). > */ > alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH); > > - if (!wait) { > + if (atomic) { > /* > - * Not worth trying to allocate harder for > - * __GFP_NOMEMALLOC even if it can't schedule. > + * Not worth trying to allocate harder for __GFP_NOMEMALLOC even > + * if it can't schedule. > */ > - if (!(gfp_mask & __GFP_NOMEMALLOC)) > + if (!(gfp_mask & __GFP_NOMEMALLOC)) > alloc_flags |= ALLOC_HARDER; > /* > - * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc. > - * See also cpuset_zone_allowed() comment in kernel/cpuset.c. > + * Ignore cpuset mems for GFP_ATOMIC rather than fail, see the > + * comment for __cpuset_node_allowed_softwall(). > */ > alloc_flags &= ~ALLOC_CPUSET; > } else if (unlikely(rt_task(current)) && !in_interrupt()) > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to [email protected]. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"[email protected]";> [email protected] </a> -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
