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This combined responsibility can= lead >>>>> to significant performance bottlenecks, especially under high memor= y >>>>> pressure. The kswapd thread becomes a single point of contention, c= ausing >>>>> delays in memory reclaiming and overall system performance degradat= ion. >>>>> >>>>> Solution: >>>>> Introduced kcompressd to handle asynchronous compression during mem= ory >>>>> reclaim, improving efficiency by offloading compression tasks from >>>>> kswapd. This allows kswapd to focus on its primary task of page rec= laim >>>>> without being burdened by the additional overhead of compression. >>>>> >>>>> In our handheld devices, we found that applying this mechanism under = high >>>>> memory pressure scenarios can increase the rate of pgsteal_anon per s= econd >>>>> by over 260% compared to the situation with only kswapd. Additionally= , we >>>>> observed a reduction of over 50% in page allocation stall occurrences= , >>>>> further demonstrating the effectiveness of kcompressd in alleviating = memory >>>>> pressure and improving system responsiveness. >>>>> >>>>> Co-developed-by: Barry Song <21cnbao@gmail.com> >>>>> Signed-off-by: Barry Song <21cnbao@gmail.com> >>>>> Signed-off-by: Qun-Wei Lin >>>>> Reference: Re: [PATCH 0/2] Improve Zram by separating compression con= text from kswapd - Barry Song >>>>> https://lore.kernel.org/lkml/20250313093005.13998-1-21cnbao@= gmail.com/ >>>>> --- >>>> >>>> +Cc Zi Yan, who might be interested in writing a framework (or improvi= ng >>>> the existing one, padata) for parallelizing jobs (e.g. migration/compr= ession) >>> >>> Thanks. >>> >>> I am currently looking into padata [1] to perform multithreaded page mi= gration > > TIL about padata :) > >>> copy job. But based on this patch, it seems that kcompressed is just an= additional >>> kernel thread of executing zswap_store(). Is there any need for perform= ing >>> compression with multiple threads? >> >> The current focus is on enabling kswapd to perform asynchronous compress= ion, >> which can significantly reduce direct reclaim and allocstall events. >> Therefore, the work begins with supporting a single thread. Supporting >> multiple threads might be possible in the future, but it could be diffic= ult >> to control=E2=80=94especially on busy phones=E2=80=94since it consumes m= ore power and may >> interfere with other threads impacting user experience. > > Right, yeah. > >> >>> >>> BTW, I also notice that zswap IAA compress batching patchset[2] is usin= g >>> hardware accelerator (Intel Analytics Accelerator) to speed up zswap. >>> I wonder if the handheld devices have similar hardware to get a similar= benefit. >> >> Usually, the answer is no. We use zRAM and CPU, but this patch aims to p= rovide >> a common capability that can be shared by both zRAM and zswap. >> > > Also, not everyone and every setup has access to hardware compression > accelerators :) This provides benefits for all users. Got it. Thanks for the explanation. -- Best Regards, Yan, Zi