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Date: Thu, 18 Jan 2024 13:52:31 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Chris Li <chrisl@kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Wei =?utf-8?B?WHXvv7w=?= <weixugc@google.com>,
	Yu Zhao <yuzhao@google.com>, Greg Thelen <gthelen@google.com>,
	Chun-Tse Shao <ctshao@google.com>,
	Suren =?utf-8?B?QmFnaGRhc2FyeWFu77+8?= <surenb@google.com>,
	Brain Geffon <bgeffon@google.com>, Minchan Kim <minchan@kernel.org>,
	Michal Hocko <mhocko@suse.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Huang Ying <ying.huang@intel.com>, Nhat Pham <nphamcs@gmail.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Kairui Song <kasong@tencent.com>,
	Zhongkun He <hezhongkun.hzk@bytedance.com>,
	Kemeng Shi <shikemeng@huaweicloud.com>,
	Barry Song <v-songbaohua@oppo.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Chengming Zhou <zhouchengming@bytedance.com>
Subject: Re: [PATCH 1/2] mm: zswap.c: add xarray tree to zswap
Message-ID: <ZaktH7xc72x4Xr3d@casper.infradead.org>
References: <20240117-zswap-xarray-v1-0-6daa86c08fae@kernel.org>
 <20240117-zswap-xarray-v1-1-6daa86c08fae@kernel.org>
 <CAJD7tkYEx57CPBoaN9GW4M3Mx-+jEsOMWJ02nLKSKD-MLb-WPA@mail.gmail.com>
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On Wed, Jan 17, 2024 at 10:20:29PM -0800, Yosry Ahmed wrote:
> >         /* walk the tree and free everything */
> >         spin_lock(&tree->lock);
> > +
> > +       xas_for_each(&xas, e, ULONG_MAX)
> 
> Why not use xa_for_each?

xas_for_each() is O(n) while xa_for_each() is O(n log n), as mentioned
in the fine documentation.  If you don't need to drop the lock while
in the body of the loop, always prefer xas_for_each().