Re: [RFC PATCH 0/3] Introduce per-cgroup compression priority

Hi Jinji,

On Sun, Oct 26, 2025 at 01:05:07AM +0000, jinji zhong wrote:
> Hello everyone,
> 
> On Android, different applications have varying tolerance for
> decompression latency. Applications with higher tolerance for
> decompression latency are better suited for algorithms like ZSTD,
> which provides high compression ratio but slower decompression
> speed. Conversely, applications with lower tolerance for
> decompression latency can use algorithms like LZ4 or LZO that
> offer faster decompression but lower compression ratios. For example,
> lightweight applications (with few anonymous pages) or applications
> without foreground UI typically have higher tolerance for decompression
> latency.
> 
> Similarly, in memory allocation slow paths or under high CPU
> pressure, using algorithms with faster compression speeds might
> be more appropriate.
> 
> This patch introduces a per-cgroup compression priority mechanism,
> where different compression priorities map to different algorithms.
> This allows administrators to select appropriate compression
> algorithms on a per-cgroup basis.
> 
> Currently, this patch is experimental and we would greatly
> appreciate community feedback. I'm uncertain whether obtaining
> compression priority via get_cgroup_comp_priority in zram is the
> best approach. While this implementation is convenient, it seems
> somewhat unusual. Perhaps the next step should be to pass
> compression priority through page->private.
> 

Setting aside the issues in the implementation (like changing
compression algorithm of a cgroup while it already has some memory
compressed using older algo), I don't think memcg interface is the right
way to go about it. We usually add interfaces to memcg that have
hierarchical semantics.

Anyways if you want to have this feature, I think BPF might be the way
to get this flexibility without introducing any stable API and then you
can experiment and evaluate if this really helps.