Re: [PATCH 35/40] lib: implement context capture support for tagged allocations

Michal Hocko
2023-05-04T08:13:41Z

On Wed 03-05-23 08:24:19, Suren Baghdasaryan wrote:
> On Wed, May 3, 2023 at 12:39 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 01-05-23 09:54:45, Suren Baghdasaryan wrote:
> > [...]
> > > +struct codetag_ctx *alloc_tag_create_ctx(struct alloc_tag *tag, size_t size)
> > > +{
> > > + struct alloc_call_ctx *ac_ctx;
> > > +
> > > + /* TODO: use a dedicated kmem_cache */
> > > + ac_ctx = kmalloc(sizeof(struct alloc_call_ctx), GFP_KERNEL);
> >
> > You cannot really use GFP_KERNEL here. This is post_alloc_hook path and
> > that has its own gfp context.
>
> I missed that. Would it be appropriate to use the gfp_flags parameter
> of post_alloc_hook() here?

No. the original allocation could have been GFP_USER based and you do
not want these allocations to pullute other zones potentially. You want
GFP_KERNEL compatible subset of that mask.

But even then I really detest an additional allocation from this context
for every single allocation request. There GFP_NOWAIT allocation for
steckdepot but that is at least cached and generally not allocating.
This will allocate for every single allocation. There must be a better
way.
--
Michal Hocko
SUSE Labs