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

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Message-ID: <ZFNoVfb+1W4NAh74@dhcp22.suse.cz>
Date:   Thu, 4 May 2023 10:09:57 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH 35/40] lib: implement context capture support for tagged
 allocations

On Wed 03-05-23 08:24:19, Suren Baghdasaryan wrote:
> On Wed, May 3, 2023 at 12:39 AM Michal Hocko <mhocko@...e.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