From: Michal Hocko <mhocko@suse.com>
To: Jaewon Kim <jaewon31.kim@samsung.com>
Cc: "jstultz@google.com" <jstultz@google.com>,
"tjmercier@google.com" <tjmercier@google.com>,
"sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
"daniel.vetter@ffwll.ch" <daniel.vetter@ffwll.ch>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jaewon31.kim@gmail.com" <jaewon31.kim@gmail.com>
Subject: Re: [PATCH v3] dma-buf/heaps: system_heap: avoid too much allocation
Date: Wed, 12 Apr 2023 13:02:59 +0200 [thread overview]
Message-ID: <ZDaP4/PYyb9tKGQi@dhcp22.suse.cz> (raw)
In-Reply-To: <20230412094440epcms1p445319579ead0d0576bb616ebb07501b4@epcms1p4>
On Wed 12-04-23 18:44:40, Jaewon Kim wrote:
> >On Wed 12-04-23 17:57:26, Jaewon Kim wrote:
> >> >Sorry for being late. I know there was some pre-existing discussion
> >> >around that but I didn't have time to participate.
> >> >
> >> >On Mon 10-04-23 16:32:28, Jaewon Kim wrote:
> >> >> @@ -350,6 +350,9 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
> >> >> struct page *page, *tmp_page;
> >> >> int i, ret = -ENOMEM;
> >> >>
> >> >> + if (len / PAGE_SIZE > totalram_pages())
> >> >> + return ERR_PTR(-ENOMEM);
> >> >> +
> >> >
> >> >This is an antipattern imho. Check 7661809d493b ("mm: don't allow
> >> >oversized kvmalloc() calls") how kvmalloc has dealt with a similar
> >>
> >> Hello Thank you for the information.
> >>
> >> I tried to search the macro of INT_MAX.
> >>
> >> include/vdso/limits.h
> >> #define INT_MAX ((int)(~0U >> 1))
> >>
> >> AFAIK the dma-buf system heap user can request that huge size more than 2GB.
> >
> >Do you have any pointers? This all is unreclaimable memory, right? How
> >are those users constrained to not go overboard?
>
> Correct dma-buf system heap memory is unreclaimable. To avoid that huge request,
> this patch includes __GFP_RETRY_MAYFAIL.
__GFP_RETRY_MAYFAIL doesn't avoud huge requests. It will drain the free
available memory to the edge of OOM (especially for low order requests)
so effectively anybody else requesting any memory (GFP_KERNEL like req.)
will hit the oom killer very likely).
> #define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO | __GFP_RETRY_MAYFAIL)
>
> >
> >> So
> >> I think totalram_pages() is better than INT_MAX in this case.
> >>
> >> >issue. totalram_pages doesn't really tell you anything about incorrect
> >> >users. You might be on a low memory system where the request size is
> >> >sane normally, it just doesn't fit into memory on that particular
> >> >machine.
> >>
> >> Sorry maybe I'm not fully understand what you meant. User may requested
> >> a huge size like 3GB on 2GB ram device. But I think that should be rejected
> >> because it is bigger than the device ram size.
> >
> >Even totalram_pages/10 can be just unfeasible amount of data to be
> >allocated without a major disruption. totalram_pages is no measure of
> >the memory availability.
> >If you want to have a ballpark estimation then si_mem_available might be
> >something you are looking for. But I thought the sole purpose of this
> >patch is to catch obviously buggy callers (like sign overflow lenght
> >etc) rather than any memory consumption sanity check.
>
> Yes if we want to avoid some big size, si_mem_available could be one option.
> Actually I tried to do totalram_pages() / 2 like the old ion system heap in
> the previous patch version. Anyway totalram_pages in this patch is used to
> avoid the buggy size.
So let me repeat that totalram_pages is a wrong thing to do(tm).
This is not a subsystem I would feel like nacking a patch, but consider
this feedback as strong of a rejection as somebody external can give
you. A mm internal allocator would get an outright nack.
What you are doing is just wrong and an antipattern to what other
allocators do. Either use something like INT_MAX to catch overflows or
do not try to catch buggy code but pretend a better memory consumer
citizen by using something like si_mem_available (ideally think of
other potential memory users so do not allow any request to use all
of it). The later might require much more involved interface and I do
rememeber some attempts to account and limit dmabuf memory better.
> And as we discussed in v2 patch, __GFP_RETRY_MAYFAIL was added. And I think
> the gfp makes us feel better in memory perspective.
wishful thinking that is.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2023-04-12 11:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcas1p4.samsung.com>
2023-04-10 7:32 ` [PATCH v3] dma-buf/heaps: system_heap: avoid too much allocation Jaewon Kim
2023-04-12 8:22 ` Michal Hocko
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p7>
2023-04-12 8:57 ` Jaewon Kim
2023-04-12 9:23 ` Michal Hocko
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p4>
2023-04-12 9:44 ` Jaewon Kim
2023-04-12 11:02 ` Michal Hocko [this message]
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p8>
2023-04-12 11:37 ` Jaewon Kim
2023-04-12 11:51 ` Michal Hocko
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p2>
2023-04-12 12:35 ` Jaewon Kim
2023-04-12 13:01 ` Michal Hocko
2023-04-12 16:49 ` T.J. Mercier
2023-04-12 22:10 ` Jaewon Kim
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p6>
2023-04-13 0:16 ` Jaewon Kim
2023-04-13 6:55 ` Michal Hocko
[not found] ` <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p1>
2023-04-13 7:01 ` Jaewon Kim
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