linux-kernel - Re: [PATCH 0/2] RFC: zswap tree use xarray instead of RB tree

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Date: Thu, 18 Jan 2024 21:14:14 -0800
From: Chris Li <chriscli@...gle.com>
To: Nhat Pham <nphamcs@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Wei Xu <weixugc@...gle.com>, 
	Yu Zhao <yuzhao@...gle.com>, Greg Thelen <gthelen@...gle.com>, 
	Chun-Tse Shao <ctshao@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Yosry Ahmed <yosryahmed@...gle.com>, Brain Geffon <bgeffon@...gle.com>, 
	Minchan Kim <minchan@...nel.org>, Michal Hocko <mhocko@...e.com>, 
	Mel Gorman <mgorman@...hsingularity.net>, Huang Ying <ying.huang@...el.com>, 
	Johannes Weiner <hannes@...xchg.org>, Kairui Song <kasong@...cent.com>, 
	Zhongkun He <hezhongkun.hzk@...edance.com>, Kemeng Shi <shikemeng@...weicloud.com>, 
	Barry Song <v-songbaohua@...o.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Joel Fernandes <joel@...lfernandes.org>, 
	Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH 0/2] RFC: zswap tree use xarray instead of RB tree

On Thu, Jan 18, 2024 at 10:01 AM Nhat Pham <nphamcs@...il.com> wrote:
>
> On Wed, Jan 17, 2024 at 7:06 PM Chris Li <chrisl@...nel.org> wrote:
> >
> > The RB tree shows some contribution to the swap fault
> > long tail latency due to two factors:
> > 1) RB tree requires re-balance from time to time.
> > 2) The zswap RB tree has a tree level spin lock protecting
> > the tree access.
> >
> > The swap cache is using xarray. The break down the swap
> > cache access does not have the similar long time as zswap
> > RB tree.
> >
> > Moving the zswap entry to xarray enable read side
> > take read RCU lock only.
> >
> > The first patch adds the xarray alongside the RB tree.
> > There is some debug check asserting the xarray agrees with
> > the RB tree results.
> >
> > The second patch removes the zwap RB tree.
> >
> > I expect to merge the zswap rb tree spin lock with the xarray
> > lock in the follow up changes.
> >
> > I can surely use some help in reviewing and testing.
> >
> > Signed-off-by: Chris Li <chrisl@...nel.org>
> > ---
> > Chris Li (2):
> >       mm: zswap.c: add xarray tree to zswap
>
> While I think it is pretty neat to keep the rbtree around to check if
> the results agree during development stages, in the final version
> please squash the patches. One patch is enough :)

Ack.

Chris