linux-kernel - Re: [PATCH 1/2] mm: zswap.c: add xarray tree to zswap

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Date: Fri, 19 Jan 2024 14:05:36 -0800
From: Chris Li <chriscli@...gle.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>, 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>, 
	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>, 
	Nhat Pham <nphamcs@...il.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>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Joel Fernandes <joel@...lfernandes.org>, Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH 1/2] mm: zswap.c: add xarray tree to zswap

Hi Yosry,

On Fri, Jan 19, 2024 at 1:41 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> > if your code is naturally structured so that you delete the entries
> > after freeing them, you have no reason to call xa_destroy().
>
> Thanks for elaborating. Based on this, I believe doing xas_for_each()
> { zswap_free_entry(); }; xa_destroy(); is both closer to the current
> code structure and more efficient.
>
Can't do that in this case though.  Because you get the RCU read lock
on the tree.
Other threads can still lookup the xarray (also RCU read lock) and get
a pointer to the already freed memory.

Chris