Re: [patch 3/9] no PF_MEMALLOC tinkering

[Nick Piggin]

Andrew Morton wrote:
> Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
>
> > PF_MEMALLOC is really not a tool for tinkering. It is pretty specifically
> > used to prevent recursion into page reclaim, and to prevent low memory
> > deadlocks.
> >
> > The mm/swap_state.c code was the only legitimate tinkerer. Its concern
> > was addressed by the previous patch.
>
>
> What previous patch?  radix tree allocation doesn't use mempools, so this
> patch will cause add_to_swap() to oom the machine with radix tree node
> allocations.

Sorry, just assumed they did fromt that comment.

> Now if we were to add __GFP_NOMEMALLOC in add_to_swap() then things would
> work as we want them to.

That would be good.

> The dm_crypt change looks OK.
>
>
> The code in mpage.c is saying "if we failed to allocate a correctly-sized
> bvec and if we're doing pageout then try to allocate a smaller-sized bvec
> instead".
>
> It's probably fairly useless, but afaict there's nothing in any of the
> other patches here which makes it redundant.

Well, I didn't like it because it uses mempools anyway, so it
might as well just wait for its allocation.

My motivation is to remove all external users of PF_MEMALLOC,
really.

But it looks like in this case, the code is dead anyway, because
mempool_alloc will never return NULL if it is passed __GFP_WAIT.

--
SUSE Labs, Novell Inc.

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