diff options
| author | Hugh Dickins <hughd@google.com> | 2017-10-13 12:10:00 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-01-05 15:44:25 +0100 |
| commit | d41f46f778951b0ea851ca52b88b2549c6336b47 (patch) | |
| tree | 7c4cb899305a27522f268f456715f1a7579c9893 | |
| parent | fc8334e6b3e5d28afd4eec8a74493933f73b2784 (diff) | |
kaiser: _pgd_alloc() without __GFP_REPEAT to avoid stalls
Synthetic filesystem mempressure testing has shown softlockups, with
hour-long page allocation stalls, and pgd_alloc() trying for order:1
with __GFP_REPEAT in one of the backtraces each time.
That's _pgd_alloc() going for a Kaiser double-pgd, using the __GFP_REPEAT
common to all page table allocations, but actually having no effect on
order:0 (see should_alloc_oom() and should_continue_reclaim() in this
tree, but beware that ports to another tree might behave differently).
Order:1 stack allocation has been working satisfactorily without
__GFP_REPEAT forever, and page table allocation only asks __GFP_REPEAT
for awkward occasions in a long-running process: it's not appropriate
at fork or exec time, and seems to be doing much more harm than good:
getting those contiguous pages under very heavy mempressure can be
hard (though even without it, Kaiser does generate more mempressure).
Mask out that __GFP_REPEAT inside _pgd_alloc(). Why not take it out
of the PGALLOG_GFP altogether, as v4.7 commit a3a9a59d2067 ("x86: get
rid of superfluous __GFP_REPEAT") did? Because I think that might
make a difference to our page table memcg charging, which I'd prefer
not to interfere with at this time.
hughd adds: __alloc_pages_slowpath() in the 4.4.89-stable tree handles
__GFP_REPEAT a little differently than in prod kernel or 3.18.72-stable,
so it may not always be exactly a no-op on order:0 pages, as said above;
but I think still appropriate to omit it from Kaiser or non-Kaiser pgd.
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/mm/pgtable.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index e2bd5c81279e..d0a424988f82 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -6,7 +6,7 @@ #include <asm/fixmap.h> #include <asm/mtrr.h> -#define PGALLOC_GFP GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO +#define PGALLOC_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO) #ifdef CONFIG_HIGHPTE #define PGALLOC_USER_GFP __GFP_HIGHMEM @@ -354,7 +354,9 @@ static inline void _pgd_free(pgd_t *pgd) static inline pgd_t *_pgd_alloc(void) { - return (pgd_t *)__get_free_pages(PGALLOC_GFP, PGD_ALLOCATION_ORDER); + /* No __GFP_REPEAT: to avoid page allocation stalls in order-1 case */ + return (pgd_t *)__get_free_pages(PGALLOC_GFP & ~__GFP_REPEAT, + PGD_ALLOCATION_ORDER); } static inline void _pgd_free(pgd_t *pgd) |