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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20230111052515.53941-5-zhujia.zj@bytedance.com>
References: <20230111052515.53941-5-zhujia.zj@bytedance.com> <20230111052515.53941-1-zhujia.zj@bytedance.com>
To:     Jia Zhu <zhujia.zj@bytedance.com>
Cc:     dhowells@redhat.com, linux-cachefs@redhat.com,
        linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xin Yin <yinxin.x@bytedance.com>,
        Jingbo Xu <jefflexu@linux.alibaba.com>
Subject: Re: [PATCH V4 4/5] cachefiles: narrow the scope of triggering EPOLLIN events in ondemand mode
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Content-ID: <133077.1680013145.1@warthog.procyon.org.uk>
Date:   Tue, 28 Mar 2023 15:19:05 +0100
Message-ID: <133078.1680013145@warthog.procyon.org.uk>
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Jia Zhu <zhujia.zj@bytedance.com> wrote:

> +		if (!xa_empty(xa)) {
> +			xa_lock(xa);
> +			xa_for_each_marked(xa, index, req, CACHEFILES_REQ_NEW) {
> +				if (!cachefiles_ondemand_is_reopening_read(req)) {
> +					mask |= EPOLLIN;
> +					break;
> +				}
> +			}
> +			xa_unlock(xa);
> +		}

I wonder if there's a more efficient way to do this.  I guess it depends on
how many reqs you expect to get in a queue.  It might be worth taking the
rcu_read_lock before calling xa_lock() and holding it over the whole loop.

David