From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: [RFC 1/4] fs: Add generic file system event notifications
Date: Wed, 15 Apr 2015 22:46:23 -0500
Message-ID: <552F308F.1050505@redhat.com>
References: <1429082147-4151-1-git-send-email-b.michalska@samsung.com> <1429082147-4151-2-git-send-email-b.michalska@samsung.com>
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Cc: tytso@mit.edu, adilger.kernel@dilger.ca, hughd@google.com,
        lczerner@redhat.com, hch@infradead.org, linux-ext4@vger.kernel.org,
        linux-mm@kvack.org, kyungmin.park@samsung.com, kmpark@infradead.org
To: Beata Michalska <b.michalska@samsung.com>, linux-kernel@vger.kernel.org
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In-Reply-To: <1429082147-4151-2-git-send-email-b.michalska@samsung.com>
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On 4/15/15 2:15 AM, Beata Michalska wrote:
> Introduce configurable generic interface for file
> system-wide event notifications to provide file
> systems with a common way of reporting any potential
> issues as they emerge.
>=20
> The notifications are to be issued through generic
> netlink interface, by a dedicated, for file system
> events, multicast group. The file systems might as
> well use this group to send their own custom messages.

...

> + 4.3 Threshold notifications:
> +
> + #include <linux/fs_event.h>
> + void fs_event_alloc_space(struct super_block *sb, u64 ncount);
> + void fs_event_free_space(struct super_block *sb, u64 ncount);
> +
> + Each filesystme supporting the treshold notifiactions should call
> + fs_event_alloc_space/fs_event_free_space repsectively whenever the
> + ammount of availbale blocks changes.
> + - sb:     the filesystem's super block
> + - ncount: number of blocks being acquired/released

so:

> +void fs_event_alloc_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +	s64 count;
> +
> +	spin_lock(&fs_trace_lock);

Every allocation/free for every supported filesystem system-wide will be
serialized on this global spinlock?  That sounds like a non-starter...

-Eric

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