Messages in this thread | | | From | Dmitry Vyukov <> | Date | Fri, 20 Apr 2018 19:52:58 +0200 | Subject | Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask |
| |
On Fri, Apr 20, 2018 at 7:50 PM, Catalin Marinas <catalin.marinas@arm.com> wrote: > On Sat, Apr 21, 2018 at 12:58:33AM +0800, Chunyu Hu wrote: >> __GFP_NORETRY and __GFP_NOFAIL are combined in gfp_kmemleak_mask now. >> But it's a wrong combination. As __GFP_NOFAIL is blockable, but >> __GFP_NORETY is not blockable, make it self-contradiction. >> >> __GFP_NOFAIL means 'The VM implementation _must_ retry infinitely'. But >> it's not the real intention, as kmemleak allow alloc failure happen in >> memory pressure, in that case kmemleak just disables itself. > > Good point. The __GFP_NOFAIL flag was added by commit d9570ee3bd1d > ("kmemleak: allow to coexist with fault injection") to keep kmemleak > usable under fault injection. > >> commit 9a67f6488eca ("mm: consolidate GFP_NOFAIL checks in the allocator >> slowpath") documented that what user wants here should use GFP_NOWAIT, and >> the WARN in __alloc_pages_slowpath caught this weird usage. >> >> <snip> >> WARNING: CPU: 3 PID: 64 at mm/page_alloc.c:4261 __alloc_pages_slowpath+0x1cc3/0x2780 > [...] >> Replace the __GFP_NOFAIL with GFP_NOWAIT in gfp_kmemleak_mask, __GFP_NORETRY >> and GFP_NOWAIT are in the gfp_kmemleak_mask. So kmemleak object allocaion >> is no blockable and no reclaim, making kmemleak less disruptive to user >> processes in pressure. > > It doesn't solve the fault injection problem for kmemleak (unless we > change __should_failslab() somehow, not sure yet). An option would be to > replace __GFP_NORETRY with __GFP_NOFAIL in kmemleak when fault injection > is enabled. > > BTW, does the combination of NOWAIT and NORETRY make kmemleak > allocations more likely to fail? > > Cc'ing Dmitry as well.
Yes, it would be bad if there allocations fail due to fault injection. These are both debugging tools and ideally should not interfere.
>> Signed-off-by: Chunyu Hu <chuhu@redhat.com> >> CC: Michal Hocko <mhocko@suse.com> >> --- >> mm/kmemleak.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/kmemleak.c b/mm/kmemleak.c >> index 9a085d5..4ea07e4 100644 >> --- a/mm/kmemleak.c >> +++ b/mm/kmemleak.c >> @@ -126,7 +126,7 @@ >> /* GFP bitmask for kmemleak internal allocations */ >> #define gfp_kmemleak_mask(gfp) (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \ >> __GFP_NORETRY | __GFP_NOMEMALLOC | \ >> - __GFP_NOWARN | __GFP_NOFAIL) >> + __GFP_NOWARN | GFP_NOWAIT) >> >> /* scanning area inside a memory block */ >> struct kmemleak_scan_area { >> -- >> 1.8.3.1
| |