[PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Mikulas Patocka]

The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
flags") breaks the device mapper VDO target. The VDO target calls vmalloc
with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
flags.

There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
let's add this flag to GFP_VMALLOC_SUPPORTED.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Fixes: 07003531e03c ("mm/vmalloc: warn on invalid vmalloc gfp flags")
Cc: stable@vger.kernel.org	# v6.19

---
 mm/vmalloc.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6/mm/vmalloc.c
===================================================================
--- linux-2.6.orig/mm/vmalloc.c
+++ linux-2.6/mm/vmalloc.c
@@ -3928,6 +3928,7 @@ fail:
  */
 #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
 				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY |\
+				__GFP_RETRY_MAYFAIL |\
 				GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
 				GFP_USER | __GFP_NOLOCKDEP)
 

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[SeongJae Park]

On Thu, 12 Feb 2026 17:33:30 +0100 (CET) Mikulas Patocka <mpatocka@redhat.com> wrote:

> The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
> flags") breaks the device mapper VDO target. The VDO target calls vmalloc
> with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
> flags.
> 
> There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
> let's add this flag to GFP_VMALLOC_SUPPORTED.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
> Fixes: 07003531e03c ("mm/vmalloc: warn on invalid vmalloc gfp flags")
> Cc: stable@vger.kernel.org	# v6.19

Acked-by: SeongJae Park <sj@kernel.org>

> 
> ---
>  mm/vmalloc.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-2.6/mm/vmalloc.c
> ===================================================================
> --- linux-2.6.orig/mm/vmalloc.c
> +++ linux-2.6/mm/vmalloc.c
> @@ -3928,6 +3928,7 @@ fail:
>   */
>  #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
>  				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY |\
> +				__GFP_RETRY_MAYFAIL |\
>  				GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
>  				GFP_USER | __GFP_NOLOCKDEP)

By the way, I think this list might better to be alphabetically sorted in
future.  Obviously just a trivial and random thought that never required for
this patch.


Thanks,
SJ

[...]

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Anshuman Khandual]

On 21/02/26 6:49 AM, SeongJae Park wrote:
> On Thu, 12 Feb 2026 17:33:30 +0100 (CET) Mikulas Patocka <mpatocka@redhat.com> wrote:
> 
>> The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
>> flags") breaks the device mapper VDO target. The VDO target calls vmalloc
>> with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
>> flags.
>>
>> There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
>> let's add this flag to GFP_VMALLOC_SUPPORTED.
>>
>> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>> Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
>> Fixes: 07003531e03c ("mm/vmalloc: warn on invalid vmalloc gfp flags")
>> Cc: stable@vger.kernel.org	# v6.19
> 
> Acked-by: SeongJae Park <sj@kernel.org>
> 
>>
>> ---
>>  mm/vmalloc.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> Index: linux-2.6/mm/vmalloc.c
>> ===================================================================
>> --- linux-2.6.orig/mm/vmalloc.c
>> +++ linux-2.6/mm/vmalloc.c
>> @@ -3928,6 +3928,7 @@ fail:
>>   */
>>  #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
>>  				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY |\
>> +				__GFP_RETRY_MAYFAIL |\
>>  				GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
>>  				GFP_USER | __GFP_NOLOCKDEP)
> 
> By the way, I think this list might better to be alphabetically sorted in

Agreed.

> future.  Obviously just a trivial and random thought that never required for
> this patch.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Vishal Moola (Oracle)]

On Thu, Feb 12, 2026 at 05:33:30PM +0100, Mikulas Patocka wrote:
> The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
> flags") breaks the device mapper VDO target. The VDO target calls vmalloc
> with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
> flags.
> 
> There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
> let's add this flag to GFP_VMALLOC_SUPPORTED.

My only skepticism about this comes from the line in the
vmalloc_node_range() doc: 
"and %__GFP_RETRY_MAYFAIL are not supported."

I myself don't know why that may be. Could you elaborate on if/why the
doc is wrong please?

> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
> Fixes: 07003531e03c ("mm/vmalloc: warn on invalid vmalloc gfp flags")
> Cc: stable@vger.kernel.org	# v6.19
> 
> ---
>  mm/vmalloc.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-2.6/mm/vmalloc.c
> ===================================================================
> --- linux-2.6.orig/mm/vmalloc.c
> +++ linux-2.6/mm/vmalloc.c
> @@ -3928,6 +3928,7 @@ fail:
>   */
>  #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
>  				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY |\
> +				__GFP_RETRY_MAYFAIL |\
>  				GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
>  				GFP_USER | __GFP_NOLOCKDEP)
>  
> 

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Mikulas Patocka]

On Mon, 23 Feb 2026, Vishal Moola (Oracle) wrote:

> On Thu, Feb 12, 2026 at 05:33:30PM +0100, Mikulas Patocka wrote:
> > The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
> > flags") breaks the device mapper VDO target. The VDO target calls vmalloc
> > with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
> > flags.
> > 
> > There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
> > let's add this flag to GFP_VMALLOC_SUPPORTED.
> 
> My only skepticism about this comes from the line in the
> vmalloc_node_range() doc: 
> "and %__GFP_RETRY_MAYFAIL are not supported."
> 
> I myself don't know why that may be. Could you elaborate on if/why the
> doc is wrong please?

This statement was added by Michal Hocko in the commit 
b7d90e7a5ea8d64e668d5685925900d33d3884d5. Michal, could you explain why do 
you think that __GFP_RETRY_MAYFAIL is not supported?

The VDO module needs to allocate large amounts of memory and it doesn't 
want to trigger the OOM killer (which would kill some innocent task and 
wouldn't solve the out of memory condition at all), so I think that 
__GFP_RETRY_MAYFAIL is appropriate.

Mikulas

> > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> > Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
> > Fixes: 07003531e03c ("mm/vmalloc: warn on invalid vmalloc gfp flags")
> > Cc: stable@vger.kernel.org	# v6.19
> > 
> > ---
> >  mm/vmalloc.c |    1 +
> >  1 file changed, 1 insertion(+)
> > 
> > Index: linux-2.6/mm/vmalloc.c
> > ===================================================================
> > --- linux-2.6.orig/mm/vmalloc.c
> > +++ linux-2.6/mm/vmalloc.c
> > @@ -3928,6 +3928,7 @@ fail:
> >   */
> >  #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
> >  				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY |\
> > +				__GFP_RETRY_MAYFAIL |\
> >  				GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\
> >  				GFP_USER | __GFP_NOLOCKDEP)
> >  
> > 
> 

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Uladzislau Rezki]

On Mon, Feb 23, 2026 at 08:25:38PM +0100, Mikulas Patocka wrote:
> 
> 
> On Mon, 23 Feb 2026, Vishal Moola (Oracle) wrote:
> 
> > On Thu, Feb 12, 2026 at 05:33:30PM +0100, Mikulas Patocka wrote:
> > > The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
> > > flags") breaks the device mapper VDO target. The VDO target calls vmalloc
> > > with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
> > > flags.
> > > 
> > > There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
> > > let's add this flag to GFP_VMALLOC_SUPPORTED.
> > 
> > My only skepticism about this comes from the line in the
> > vmalloc_node_range() doc: 
> > "and %__GFP_RETRY_MAYFAIL are not supported."
> > 
> > I myself don't know why that may be. Could you elaborate on if/why the
> > doc is wrong please?
> 
> This statement was added by Michal Hocko in the commit 
> b7d90e7a5ea8d64e668d5685925900d33d3884d5. Michal, could you explain why do 
> you think that __GFP_RETRY_MAYFAIL is not supported?
> 
> The VDO module needs to allocate large amounts of memory and it doesn't 
> want to trigger the OOM killer (which would kill some innocent task and 
> wouldn't solve the out of memory condition at all), so I think that 
> __GFP_RETRY_MAYFAIL is appropriate.
> 
I do not see any problems using this with vmalloc from the first glance.
KASAN path was hard-coded when it comes to GFP but it is not anymore.
 
--
Uladzislau Rezki

Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc

[Michal Hocko]

On Mon 23-02-26 20:25:38, Mikulas Patocka wrote:
> 
> 
> On Mon, 23 Feb 2026, Vishal Moola (Oracle) wrote:
> 
> > On Thu, Feb 12, 2026 at 05:33:30PM +0100, Mikulas Patocka wrote:
> > > The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp
> > > flags") breaks the device mapper VDO target. The VDO target calls vmalloc
> > > with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed
> > > flags.
> > > 
> > > There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so 
> > > let's add this flag to GFP_VMALLOC_SUPPORTED.
> > 
> > My only skepticism about this comes from the line in the
> > vmalloc_node_range() doc: 
> > "and %__GFP_RETRY_MAYFAIL are not supported."
> > 
> > I myself don't know why that may be. Could you elaborate on if/why the
> > doc is wrong please?
> 
> This statement was added by Michal Hocko in the commit 
> b7d90e7a5ea8d64e668d5685925900d33d3884d5. Michal, could you explain why do 
> you think that __GFP_RETRY_MAYFAIL is not supported?

The problem with __GFP_RETRY_MAYFAIL is that it cannot be fully
supported. While pages that back the allocation can be easily made aware
of this failure mode there are page table allocations which are
hardocded GFP_KERNEL and there is no sensible way to extend the API to
change that (as we have learned several time over years).

> The VDO module needs to allocate large amounts of memory and it doesn't 
> want to trigger the OOM killer (which would kill some innocent task and 
> wouldn't solve the out of memory condition at all), so I think that 
> __GFP_RETRY_MAYFAIL is appropriate.

Understood. But as said the very page table allocation could be the
trigger for the unwanted OOM. The same applies to __GFP_NORETRY
unfortunately as well. vmalloc has just recently gained support of
GFP_NOWAIT allocation mode, though. This will make the allocation
failure much more likely though so I am not entirely sure this is a
proper solution for your problem.
-- 
Michal Hocko
SUSE Labs