On Fri, 06 Feb 2009 09:20:30 +0900 Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> wrote: > > At 05:05 09/02/06, Andrew Morton wrote: > >On Tue, 03 Feb 2009 17:04:40 +0900 > >Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> wrote: > > > >> I removed i_mutex from generic_file_llseek. > >> I think that the reason of protecting lseek with i_mutex is just > >> touching i_size atomically. > >> > >> So I introduce i_size_read here so i_mutex is no longer needed. > >> > >> Following patch removes i_mutex from generic_file_llseek, and deletes > >> generic_file_llseek_nolock totally. > >> > >> Currently there is i_mutex contention not only around lseek, but also > >fsync or write. > >> So, I think we can mitigate i_mutex contention between fsync lseek and > >write by > >> removing i_mutex. > > > >Prior to this change, generic_file_llseek() modified file->f_pos > >atomically with respect to other i_mutex holders. > > > >After this change, it doesn't. > > Hi Andrew. > > Even before this change is applied, file->f_pos access is not atomic. > sys_read change f_pos value through file_pos_write without i_mutex. I know. That's why I specified "with respect to other i_mutex holders". This patch makes things worse. At very very minimum the changelog should explain that this patch makes things worse, and demonstrate why this is justifiable. > I think seqlock is needed to make f_pos access atomic. Maybe. Or atomic64_t, or spinlocking, or i_mutex, or something else. -- 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
