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s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dfs5PllpQpG9QpYkVZTr5YGvpGpnNGmZTQiHA7UaSnw=; b=WxNQTC6oaA3fywFf8rJJUoFVPFFXZzK/h5KeCZf6nfba7xIzC9y7A1Lj09vzckXwPQ bv/rLABP/yRNz5pG0Gl/4xqVv6gQ3blcu8KiHNe2LZjAJPP4nI9bv7Ge1XswTOVWcY++ sJ6YTU4zdDZsoTqSM0en/0wkKCV9OvHCALRhNoTzKRjDXMWAum9z/zwxBPq8NiBE5624 TIB7doOsajVSUg5dZy6GMOi2Fo7zSXV7xxwf3jWM0pULJoOlxhqA5+xhM5GPMheYhgW5 Lx9q/7gvBIcBj6Q30vlJJOQwiLF4FpUf6F0DxRBBevJ1HH0HnWFrnyOn4U/NP/dolT0I csNg== X-Gm-Message-State: AOAM5331P7cHZ2F9qGxA+te9hBjWl9rtfngg9HF2hwL632S1Ia5rghJb 9Tn8yy0k6ajYTUaDRIBXxEJPmnv0ybtn1m1LFJw= X-Google-Smtp-Source: ABdhPJw2ZNSatUBV5nkdNWJB5epCtTEMUWyTNWezAfi/r72JR+OKrJKz92f3vb55u1hjxnOO0jazboJ+w2X3EnzYQqk= X-Received: by 2002:a05:6638:d96:: with SMTP id l22mr21113713jaj.120.1592215519677; Mon, 15 Jun 2020 03:05:19 -0700 (PDT) MIME-Version: 1.0 References: <20200612004644.255692-1-mike.kravetz@oracle.com> <20200612015842.GC23230@ZenIV.linux.org.uk> <6e8924b0-bfc4-eaf5-1775-54f506cdf623@oracle.com> In-Reply-To: From: Amir Goldstein Date: Mon, 15 Jun 2020 13:05:08 +0300 Message-ID: Subject: Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files To: Miklos Szeredi Cc: Mike Kravetz , Al Viro , Linux MM , linux-fsdevel , overlayfs , linux-kernel , Matthew Wilcox , Colin Walters , Andrew Morton , syzbot , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: C104D10008A21619 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jun 15, 2020 at 10:53 AM Miklos Szeredi wrote: > > On Sat, Jun 13, 2020 at 9:12 PM Mike Kravetz wrote: > > > > On 6/12/20 11:53 PM, Amir Goldstein wrote: > > > As a hugetlbfs developer, I do not know of a use case for interoperability > > with overlayfs. So yes, I am not too interested in making them work well > > together. However, if there was an actual use case I would be more than > > happy to consider doing the work. Just hate to put effort into fixing up > > two 'special' filesystems for functionality that may not be used. > > > > I can't speak for overlayfs developers. > > As I said, I only know of tmpfs being upper layer as a valid use case. > Does that work with hugepages? How would I go about testing that? Simple, after enabling CONFIG_HUGETLBFS: diff --git a/mount_union.py b/mount_union.py index fae8899..4070c70 100644 --- a/mount_union.py +++ b/mount_union.py @@ -15,7 +15,7 @@ def mount_union(ctx): snapshot_mntroot = cfg.snapshot_mntroot() if cfg.should_mount_upper(): system("mount " + upper_mntroot + " 2>/dev/null" - " || mount -t tmpfs upper_layer " + upper_mntroot) + " || mount -t hugetlbfs upper_layer " + upper_mntroot) layer_mntroot = upper_mntroot + "/" + ctx.curr_layer() upperdir = layer_mntroot + "/u" workdir = layer_mntroot + "/w" It fails colossally, because hugetlbfs, does not have write_iter(). It is only meant as an interface to create named maps of huge pages. So I don't really see the use case for using it as upper. Thanks, Amir.