| Message ID | 20150625001608.830BD5CA@viggo.jf.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed 24-06-15 17:16:08, Dave Hansen wrote: > > From: Dave Hansen <dave.hansen@linux.intel.com> > > According to Jan Kara: > > You can have ignored mask set without any of the > notification masks set and you are expected to clear the > ignored mask on the first IN_MODIFY event. > > But, the only way we currently have to go and find if we need to > do this ignored-mask-clearing is to go through the mark lists > and look for them. That mark list iteration requires an > srcu_read_lock() which has a memory barrier and can be expensive. > > The calculation of 'has_ignore' is pretty cheap because we store > it next to another value which we are updating and we do it > inside of a loop we were already running. > > This patch will really only matter when we have a workload where > a file is being modified often _and_ there is an active fsnotify > mark on it. Otherwise the checks against *_fsnotify.marks.first > will keep us out of the expensive srcu_read_lock() call. So this is a nice optimization but definitely not worth growing struct inode. We could use one bit in the mask itself for this though. Honza > > Cc: Jan Kara <jack@suse.cz> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: linux-fsdevel@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Tim Chen <tim.c.chen@linux.intel.com> > Cc: Andi Kleen <ak@linux.intel.com> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > --- > > b/fs/notify/fsnotify.c | 44 ++++++++++++++++++++++++++++++++++------ > b/fs/notify/mark.c | 8 +++++-- > b/include/linux/fsnotify_head.h | 1 > 3 files changed, 45 insertions(+), 8 deletions(-) > > diff -puN fs/notify/fsnotify.c~fsnotify-ignore-present fs/notify/fsnotify.c > --- a/fs/notify/fsnotify.c~fsnotify-ignore-present 2015-06-24 17:14:37.187226743 -0700 > +++ b/fs/notify/fsnotify.c 2015-06-24 17:14:37.194227057 -0700 > @@ -183,6 +183,34 @@ static int send_to_group(struct inode *t > } > > /* > + * The "logical or" of all of the marks' ->mask is kept in the > + * i/mnt_fsnotify.mask. We can check it instead of going > + * through all of the marks. fsnotify_recalc_mask() does the > + * updates. > + */ > +static int some_mark_is_interested(__u32 mask, struct inode *inode, struct mount *mnt) > +{ > + if (mask & inode->i_fsnotify.mask) > + return 1; > + if (mnt && (mask & mnt->mnt_fsnotify.mask)) > + return 1; > + return 0; > +} > + > +/* > + * fsnotify_recalc_mask() recalculates "has_ignore" whenever any > + * mark's flags change. > + */ > +static int some_mark_needs_ignore_clear(struct inode *inode, struct mount *mnt) > +{ > + if (inode->i_fsnotify.has_ignore) > + return 1; > + if (mnt && mnt->mnt_fsnotify.has_ignore) > + return 1; > + return 0; > +} > + > +/* > * This is the main call to fsnotify. The VFS calls into hook specific functions > * in linux/fsnotify.h. Those functions then in turn call here. Here will call > * out to all of the registered fsnotify_group. Those groups can then use the > @@ -205,14 +233,18 @@ int fsnotify(struct inode *to_tell, __u3 > mnt = NULL; > > /* > - * if this is a modify event we may need to clear the ignored masks > - * otherwise return if neither the inode nor the vfsmount care about > - * this type of event. > + * We must clear the (user-visible) ignored mask on the first IN_MODIFY > + * event despite the 'mask' which is passed in here. But we can safely > + * skip that step if we know there are no marks which need this action. > + * > + * We can also skip looking at the list of marks if we know that none > + * of the marks are interested in the events in our 'mask'. > */ > - if (!(mask & FS_MODIFY) && > - !(test_mask & to_tell->i_fsnotify.mask) && > - !(mnt && test_mask & mnt->mnt_fsnotify.mask)) > + if ((mask & FS_MODIFY) && !some_mark_needs_ignore_clear(to_tell, mnt)) > + return 0; > + else if (!some_mark_is_interested(test_mask, to_tell, mnt)) > return 0; > + > /* > * Optimization: srcu_read_lock() has a memory barrier which can > * be expensive. It protects walking the *_fsnotify_marks lists. > diff -puN fs/notify/mark.c~fsnotify-ignore-present fs/notify/mark.c > --- a/fs/notify/mark.c~fsnotify-ignore-present 2015-06-24 17:14:37.189226832 -0700 > +++ b/fs/notify/mark.c 2015-06-24 17:14:37.194227057 -0700 > @@ -116,10 +116,14 @@ void fsnotify_recalc_mask(struct fsnotif > { > u32 new_mask = 0; > struct fsnotify_mark *mark; > + u32 has_ignore = 0; > > - hlist_for_each_entry(mark, &fsn->marks, obj_list) > + hlist_for_each_entry(mark, &fsn->marks, obj_list) { > + if (mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY) > + has_ignore = 1; > new_mask |= mark->mask; > - > + } > + fsn->has_ignore = has_ignore; > fsn->mask = new_mask; > } > > diff -puN include/linux/fsnotify_head.h~fsnotify-ignore-present include/linux/fsnotify_head.h > --- a/include/linux/fsnotify_head.h~fsnotify-ignore-present 2015-06-24 17:14:37.190226877 -0700 > +++ b/include/linux/fsnotify_head.h 2015-06-24 17:14:37.193227012 -0700 > @@ -11,6 +11,7 @@ struct fsnotify_head { > #ifdef CONFIG_FSNOTIFY > __u32 mask; /* all events this object cares about */ > struct hlist_head marks; > + __u32 has_ignore; /* any marks has ignore set */ > #endif > }; > > _
diff -puN fs/notify/fsnotify.c~fsnotify-ignore-present fs/notify/fsnotify.c --- a/fs/notify/fsnotify.c~fsnotify-ignore-present 2015-06-24 17:14:37.187226743 -0700 +++ b/fs/notify/fsnotify.c 2015-06-24 17:14:37.194227057 -0700 @@ -183,6 +183,34 @@ static int send_to_group(struct inode *t } /* + * The "logical or" of all of the marks' ->mask is kept in the + * i/mnt_fsnotify.mask. We can check it instead of going + * through all of the marks. fsnotify_recalc_mask() does the + * updates. + */ +static int some_mark_is_interested(__u32 mask, struct inode *inode, struct mount *mnt) +{ + if (mask & inode->i_fsnotify.mask) + return 1; + if (mnt && (mask & mnt->mnt_fsnotify.mask)) + return 1; + return 0; +} + +/* + * fsnotify_recalc_mask() recalculates "has_ignore" whenever any + * mark's flags change. + */ +static int some_mark_needs_ignore_clear(struct inode *inode, struct mount *mnt) +{ + if (inode->i_fsnotify.has_ignore) + return 1; + if (mnt && mnt->mnt_fsnotify.has_ignore) + return 1; + return 0; +} + +/* * This is the main call to fsnotify. The VFS calls into hook specific functions * in linux/fsnotify.h. Those functions then in turn call here. Here will call * out to all of the registered fsnotify_group. Those groups can then use the @@ -205,14 +233,18 @@ int fsnotify(struct inode *to_tell, __u3 mnt = NULL; /* - * if this is a modify event we may need to clear the ignored masks - * otherwise return if neither the inode nor the vfsmount care about - * this type of event. + * We must clear the (user-visible) ignored mask on the first IN_MODIFY + * event despite the 'mask' which is passed in here. But we can safely + * skip that step if we know there are no marks which need this action. + * + * We can also skip looking at the list of marks if we know that none + * of the marks are interested in the events in our 'mask'. */ - if (!(mask & FS_MODIFY) && - !(test_mask & to_tell->i_fsnotify.mask) && - !(mnt && test_mask & mnt->mnt_fsnotify.mask)) + if ((mask & FS_MODIFY) && !some_mark_needs_ignore_clear(to_tell, mnt)) + return 0; + else if (!some_mark_is_interested(test_mask, to_tell, mnt)) return 0; + /* * Optimization: srcu_read_lock() has a memory barrier which can * be expensive. It protects walking the *_fsnotify_marks lists. diff -puN fs/notify/mark.c~fsnotify-ignore-present fs/notify/mark.c --- a/fs/notify/mark.c~fsnotify-ignore-present 2015-06-24 17:14:37.189226832 -0700 +++ b/fs/notify/mark.c 2015-06-24 17:14:37.194227057 -0700 @@ -116,10 +116,14 @@ void fsnotify_recalc_mask(struct fsnotif { u32 new_mask = 0; struct fsnotify_mark *mark; + u32 has_ignore = 0; - hlist_for_each_entry(mark, &fsn->marks, obj_list) + hlist_for_each_entry(mark, &fsn->marks, obj_list) { + if (mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY) + has_ignore = 1; new_mask |= mark->mask; - + } + fsn->has_ignore = has_ignore; fsn->mask = new_mask; } diff -puN include/linux/fsnotify_head.h~fsnotify-ignore-present include/linux/fsnotify_head.h --- a/include/linux/fsnotify_head.h~fsnotify-ignore-present 2015-06-24 17:14:37.190226877 -0700 +++ b/include/linux/fsnotify_head.h 2015-06-24 17:14:37.193227012 -0700 @@ -11,6 +11,7 @@ struct fsnotify_head { #ifdef CONFIG_FSNOTIFY __u32 mask; /* all events this object cares about */ struct hlist_head marks; + __u32 has_ignore; /* any marks has ignore set */ #endif };