On Thu, 2016-09-22 at 20:37 -0500, Eric W. Biederman wrote: > Ian Kent <raven@xxxxxxxxxx> writes: > > > On Thu, 2016-09-22 at 10:43 -0500, Eric W. Biederman wrote: > > > Ian Kent <raven@xxxxxxxxxx> writes: > > > > > > > Eric, Mateusz, I appreciate your spending time on this and particularly > > > > pointing > > > > out my embarrassingly stupid is_local_mountpoint() usage mistake. > > > > > > > > Please accept my apology for the inconvenience. > > > > > > > > If all goes well (in testing) I'll have follow up patches to correct > > > > this > > > > fairly > > > > soon. > > > > > > Related question. Do you happen to know how many mounts per mount > > > namespace tend to be used? It looks like it is going to be wise to put > > > a configurable limit on that number. And I would like the default to be > > > something high enough most people don't care. I believe autofs is > > > likely where people tend to use the most mounts. Yes, I agree, I did want to try and avoid changing the parameters to ->d_mamange() but passing a struct path pointer might be better in the long run anyway. > > That's a good question. > > > > I've been thinking that maybe I should have used a lookup_mnt() type check > > as I > > originally started out to, for this reason, as the mnt_namespace list looks > > to > > be a linear list. > > > > But there can be a lot of mounts, and not only due to autofs, so maybe that > > should be considered anyway. > > There are two reasons for is_local_mountpoint being the way it is. > > a) For the cases where you don't have the parent mount. > b) For the cases where you want to stop things if something is mounted > on a dentry in the local mount namespace even if it isn't mounted > on that dentry at your current mount parent. (Something that was > important to not change the semantics of the single mount namespace case). > > Both of those cases to apply to unlink, rmdir, and rename. I don't think > either of those cases apply to what autofs is trying to do. Certainly > not the second. > > So if you have the parent mount I really think you want to be using some > variation of lookup_mnt(). The fact it is rcu safe may help with some > of those weird corner cases as well. > > > The number of mounts for direct mount maps is usually not very large because > > of > > the way they are implemented, large direct mount maps can have performance > > problems. There can be anywhere from a few (likely case a few hundred) to > > less > > than 10000, plus mounts that have been triggered and not yet expired. > > > > Indirect mounts have one autofs mount at the root plus the number of mounts > > that > > have been triggered and not yet expired. > > > > The number of autofs indirect map entries can range from a few to the common > > case of several thousand and in rare cases up to between 30000 and 50000. > > I've > > not heard of people with maps larger than 50000 entries. > > > > The larger the number of map entries the greater the possibility for a large > > number of active mounts so it's not hard to expect cases of a 1000 or > > somewhat > > more active mounts. > > Fair. So at least 1000. And there can be enough mounts that a limit of > 100,000 might be necessary to give head room for the existings configurations. > > Thank you. Now I just need to wrap my head around fs/namespace.c again > and see how bad a count like that will be to maintain. > > Eric > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
