From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Miklos Szeredi <miklos@szeredi.hu>, Ian Kent <raven@themaw.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 0/3] vfs: Use an xarray instead of inserted bookmarks to scan mount list
Date: Mon, 15 Mar 2021 12:46:44 +0000 [thread overview]
Message-ID: <20210315124644.GU2577561@casper.infradead.org> (raw)
In-Reply-To: <161581005972.2850696.12854461380574304411.stgit@warthog.procyon.org.uk>
On Mon, Mar 15, 2021 at 12:07:39PM +0000, David Howells wrote:
>
> Hi Al, Miklós,
>
> Can we consider replacing the "insert cursor" approach we're currently
> using for proc files to scan the current namespace's mount list[1] with
> something that uses an xarray of mounts indexed by mnt_id?
>
> This has some advantages:
>
> (1) It's simpler. We don't need to insert dummy mount objects as
> bookmarks into the mount list and code that's walking the list doesn't
> have to carefully step over them.
>
> (2) We can use the file position to represent the mnt_id and can jump to
> it directly - ie. using seek() to jump to a mount object by its ID.
>
> (3) It might make it easier to use RCU in future to dump mount entries
> rather than having to take namespace_sem. xarray provides for the
> possibility of tagging entries to say that they're viewable to avoid
> dumping incomplete mount objects.
Usually one fully constructs the object, then inserts it into the XArray.
> But there are a number of disadvantages:
>
> (1) We have to allocate memory to maintain the xarray, which becomes more
> of a problem as mnt_id values get scattered.
mnt_id values don't seem to get particularly scattered. They're allocated
using an IDA, so they stay small (unlike someone using idr_alloc_cyclic
;-).
next prev parent reply other threads:[~2021-03-15 12:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 12:07 [RFC][PATCH 0/3] vfs: Use an xarray instead of inserted bookmarks to scan mount list David Howells
2021-03-15 12:07 ` [PATCH 1/3] vfs: Use an xarray in the mount namespace to handle /proc/mounts list David Howells
2021-03-15 12:07 ` [PATCH 2/3] vfs: Use the mounts_to_id array to do /proc/mounts and co David Howells
2021-03-15 12:54 ` Matthew Wilcox
2021-03-15 12:08 ` [PATCH 3/3] vfs: Remove mount list trawling cursor stuff David Howells
2021-03-15 12:46 ` Matthew Wilcox [this message]
2021-03-15 13:14 ` [RFC][PATCH 0/3] vfs: Use an xarray instead of inserted bookmarks to scan mount list Miklos Szeredi
2021-03-15 13:17 ` Matthew Wilcox
2021-03-15 13:41 ` David Howells
2021-03-15 14:22 ` Miklos Szeredi
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