linux-kernel - Re: [PATCH] 9p: avoid attaching writeback

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Message-ID: <20190820114927.GA12715@nautica>
Date:   Tue, 20 Aug 2019 13:49:27 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Chengguang Xu <cgxu519@...o.com.cn>
Cc:     ericvh@...il.com, lucho@...kov.net,
        v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 9p: avoid attaching writeback_fid on mmap with type
 PRIVATE

Chengguang Xu wrote on Tue, Aug 20, 2019:
> Currently on mmap cache policy, we always attach writeback_fid
> whether mmap type is SHARED or PRIVATE. However, in the use case
> of kata-container which combines 9p(Guest OS) with overlayfs(Host OS),
> this behavior will trigger overlayfs' copy-up when excute command
> inside container.

hmm, I guess this just works for non-ovl cases because sync_inode()
realizes there is nothing to sync, but the fsync at the end still
triggers the copy-up ?

Well, I guess there really is no need to flush for private mappings,
so might as well go for this; sparing an extra useless clone walk cannot
hurt.

I'll queue this up after tests, no promise on delay sorry :/
-- 
Dominique