Re: [RFC 2/3] mm/vmalloc: add support for __GFP_NOFAIL

[Michal Hocko]

On Wed 20-10-21 10:25:06, Michal Hocko wrote:
[...]
> > > The flag itself is not really necessary down there as long as we
> > > guarantee that the high level logic doesn't fail. In this case we keep
> > > retrying at __vmalloc_node_range level which should be possible to cover
> > > all callers that can control gfp mask. I was thinking to put it into
> > > __get_vm_area_node but that was slightly more hairy and we would be
> > > losing the warning which might turn out being helpful in cases where the
> > > failure is due to lack of vmalloc space or similar constrain. Btw. do we
> > > want some throttling on a retry?
> > > 
> > I think adding kind of schedule() will not make things worse and in corner
> > cases could prevent a power drain by CPU. It is important for mobile devices. 
> 
> I suspect you mean schedule_timeout here? Or cond_resched? I went with a
> later for now, I do not have a good idea for how to long to sleep here.
> I am more than happy to change to to a sleep though.

Forgot to paste the follow up I have staged currently
--- 
commit 66fea55e5543fa234692a70144cd63c7a1bca32f
Author: Michal Hocko <mhocko@xxxxxxxx>
Date:   Wed Oct 20 10:12:45 2021 +0200

    fold me "mm/vmalloc: add support for __GFP_NOFAIL"
    
    - add cond_resched

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0fb5413d9239..f7098e616883 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2944,6 +2944,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	do {
 		ret = vmap_pages_range(addr, addr + size, prot, area->pages,
 			page_shift);
+		cond_resched();
 	} while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
 
 	if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
@@ -3034,8 +3035,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		warn_alloc(gfp_mask, NULL,
 			"vmalloc error: size %lu, vm_struct allocation failed",
 			real_size);
-		if (gfp_mask & __GFP_NOFAIL)
+		if (gfp_mask & __GFP_NOFAIL) {
+			cond_resched();
 			goto again;
+		}
 		goto fail;
 	}
 

-- 
Michal Hocko
SUSE Labs