On Mon, Jun 03, 2024 at 09:20:10PM -0700, Christoph Hellwig wrote:
> On Mon, Jun 03, 2024 at 07:24:03PM +0000, Bernd Schubert wrote:
> > void *vmalloc_node(unsigned long size, int node)
> > {
> > return __vmalloc_node(size, 1, GFP_KERNEL, node,
> > __builtin_return_address(0));
> > }
> >
> >
> >
> >
> > If we wanted to avoid another export, shouldn't we better rename
> > vmalloc_user to vmalloc_node_user, add the node argument and change
> > all callers?
> >
> > Anyway, I will send the current patch separately to linux-mm and will ask
> > if it can get merged before the fuse patches.
>
> Well, the GFP flags exist to avoid needing a gazillion of variants of
> everything build around the page allocator. For vmalloc we can't, as
> Kent rightly said, support GFP_NOFS and GFP_NOIO and need to use the
> scopes instead, and we should warn about that (which __vmalloc doesn't
> and could use some fixes for).
Perhaps before going any further here, we should refresh our
memories on what the vmalloc code actually does these days?
__vmalloc_area_node() does this when mapping the pages:
/*
* page tables allocations ignore external gfp mask, enforce it
* by the scope API
*/
if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
flags = memalloc_nofs_save();
else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
flags = memalloc_noio_save();
do {
ret = vmap_pages_range(addr, addr + size, prot, area->pages,
page_shift);
if (nofail && (ret < 0))
schedule_timeout_uninterruptible(1);
} while (nofail && (ret < 0));
if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
memalloc_nofs_restore(flags);
else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
memalloc_noio_restore(flags);
IOWs, vmalloc() has obeyed GFP_NOFS/GFP_NOIO constraints properly
for since early 2022 and there isn't a need to wrap it with scopes
just to do a single constrained allocation:
commit 451769ebb7e792c3404db53b3c2a422990de654e
Author: Michal Hocko <mhocko@xxxxxxxx>
Date: Fri Jan 14 14:06:57 2022 -0800
mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc
Patch series "extend vmalloc support for constrained allocations", v2.
Based on a recent discussion with Dave and Neil [1] I have tried to
implement NOFS, NOIO, NOFAIL support for the vmalloc to make life of
kvmalloc users easier.
.....
Add support for GFP_NOFS and GFP_NOIO to vmalloc directly. All internal
allocations already comply with the given gfp_mask. The only current
exception is vmap_pages_range which maps kernel page tables. Infer the
proper scope API based on the given gfp mask.
.....
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
