Date: Sun, 29 Nov 2015 08:36:13 -0500 (EST) From: Rick Macklem <rmacklem@uoguelph.ca> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD FS <freebsd-fs@freebsd.org> Subject: Re: should mutexes be uniquely named? Message-ID: <437411622.110533552.1448804173238.JavaMail.zimbra@uoguelph.ca> In-Reply-To: <20151129092235.GZ3448@kib.kiev.ua> References: <2132881382.109600978.1448717395325.JavaMail.zimbra@uoguelph.ca> <20151128142604.GW3448@kib.kiev.ua> <1688684587.110043576.1448746844037.JavaMail.zimbra@uoguelph.ca> <20151129092235.GZ3448@kib.kiev.ua>
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Kostik wrote: > On Sat, Nov 28, 2015 at 04:40:44PM -0500, Rick Macklem wrote: > > Kostik wrote: > > > On Sat, Nov 28, 2015 at 08:29:55AM -0500, Rick Macklem wrote: > > > > Hi, > > > > > > > > I think the patches I posted last week that add "-manage-gids" are > > > > about > > > > ready for a commit to head. > > > > > > > > However, there is one place in the code where I'm not sure which is > > > > better > > > > to do: > > > > --> The code replaces a single mutex with one for each hash list head > > > > (table > > > > entry). > > > > I currently use MTX_DUPOK and call them all the same thing. > > > > or > > > > I could add a "lockname" field to the hash table enty structure and > > > > give > > > > each one a unique name (similar to what Garrett Wollman did in the > > > > kernel rpc). > > > > The only downside to this is 16bytes of storage for each hash table > > > > entry. > > > > (Admittedly, I don't think many sites would need to set the hash > > > > table > > > > size > > > > greater than a few thousand, so this isn't a lot of malloc()'d > > > > memory.) > > > Question is, why do you need to acquire two mutexes simultaneously ? > > > If mutexes protect the hash list rooted in head, then this is somewhat > > > unusual. > > > > > There are two hash tables, one hashed on names and the other uid/gid. The > > entries are linked into both of these lists. > > I suppose that I could use a different name for the "name" hash table > > entries > > vs the "uid/gid" ones, which would avoid the duplication for the common > > cases. > I think this is the easiest, together with ... > > > > > There are also a couple of infrequent cases (when new entries are being > > added > > to the cache) where, to avoid a LOR in mutex locking the above 2 hash > > tables, > > the code locks all the table entries in the one hash table before doing the > > other hash table. In this case, you will still end up with duplicates > > unless > > each lock is uniquely named. > ... using mtx_lock_flags(MTX_DUPOK), to only shut up witness where it is > neccessary. > > > > > Maybe I should use a different name for the "user/group name" hash table > > than > > the "uid/gid" one, but still allow duplicates for the infrequent cases? > Exactly. > Thanks, that's what I will do unless others post with a differing opinion. rick > > > > Thanks for any help, rick > > > > > Downside is not only the name, but also a witness overhead in the > > > non-production kernels. > > > > > > > > > > > > > > So, what do you think. Should I add the code to make the mutex names > > > > unique? > > > > > > > > Thanks in advance for any comments, rick > > > > ps: The coding change is trivial. It just involves using more > > > > malloc()'d > > > > memory. > > > > _______________________________________________ > > > > freebsd-fs@freebsd.org mailing list > > > > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > > > > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" > > > >
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