On 9/16/20 9:17 AM, Andrew Morton wrote:
On Tue, 15 Sep 2020 15:56:35 +0800 <yanfei.xu@xxxxxxxxxxxxx> wrote:
From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
alloc_mask shouldn't inherit the current task's flags when
__alloc_pages_nodemask is invoked in interrupt.
...
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4889,7 +4889,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
* from a particular context which has been marked by
* memalloc_no{fs,io}_{save,restore}.
*/
- alloc_mask = current_gfp_context(gfp_mask);
+ if (!in_interrupt())
+ alloc_mask = current_gfp_context(gfp_mask);
ac.spread_dirty_pages = false;
/*
hm, yes, and perhaps other callsites in page_alloc.c.
I assume this doesn't actually make any runtime difference? Because
gfp_mask in interrupt contexts isn't going to have __GFP_IO or __GFP_FS
anyway.
Thanks for your reply!
Yes, It doesn't make any runtime difference. Theoretically, GPF_ATOMIC
or GFP_NOWAIT should be used in interrupt context for allocate pages, so
that gfp_mask isn't going to have __GFP_IO or __GFP_FS.
But if somebody use wrong gfp_masks, __GFP_IO or __GFP_FS will be
introduced, with the process interrupted has PF_MEMALLOC_NOIO or
PF_MEMALLOC_NOFS, current_gfp_context may help to hide these wrong
usages. I don't think it is the original purpose of that piece of
codes.
And how about add BUG_ON or WARN_ON to figure out the situation which
introduce __GFP_IO or __GFP_FS in interrupt context?
Regards,
Yanfei
