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

[zhongjinji <zhongjinji@honor.com>]

> 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

Zram uses flags to track the compression priority of each page,
which should be ok when the page is decompressed.

> 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.

Thanks a lot, Shakeel. I got it.

> 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.