Re: Excessive page cache occupies DMA32 memory

[Hillf Danton <hdanton@sina.com>]

On Wed, 10 Sep 2025 16:23:37 +0500 Muhammad Usama Anjum wrote:
> >>>> For example, in the mhi driver, the failure is triggered when the
> >>>> MHI's st_worker gets scheduled-in at resume.
> >>>>
> >>>> mhi_pm_st_worker()
> >>>> -> mhi_fw_load_handler()
> >>>>     -> mhi_load_image_bhi()
> >>>>        -> mhi_alloc_bhi_buffer()
> >>>>           -> dma_alloc_coherent(GFP_KERNEL) returns -ENOMEM
> >>>
> >>> And what is the exact size you are asking for here?
> > 
> > 512 KB
> > 
Any order above PAGE_ALLOC_COSTLY_ORDER is not guaranteed in 90+% cases.
Nor is it DMA32 specific.

> Another update:
> This issue reproduces on v6.11.11. To summarize, we're unable to reproduce
> this bug in the v6.15.9. We wanted to do bisection and find out which kernel
> change has caused/fixed it, but it's too difficult considering the complex
> reproducer setup (Tekken 8 Demo game + page cache stress). We don't want to
> spend more time on something that is very hard to reproduce and is already
> fixed in later versions.
> 
> My debugging has shown in v6.15.9 that the allocation succeeds under the same
> constraints of power management. My hunch is that somehow the dma memory

Can you try again without the JW work [1] applied?

> doesn't get occupied to the extent that dma allocations start to fail at
> resume in v6.15.9.
> 
> ---
> Thanks,
> Usama
>
[1] Subject: [PATCH 0/5] mm: reliable huge page allocator
https://lore.kernel.org/all/20250313210647.1314586-1-hannes@cmpxchg.org/