| Message ID | 20230408142517.800549-1-qiang1.zhang@intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3] rcu/kvfree: Prevents cache growing when the backoff_page_cache_fill is set | expand |
On Sat, Apr 08, 2023 at 10:25:17PM +0800, Zqiang wrote: > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > executed before kfree_rcu_monitor() to drain page cache, if the bnode > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > page cache again in kfree_rcu_monitor(), this commit add a check > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > if the krcp structure's->backoff_page_cache_fill is set, prevent page > cache growing and disable allocated page in fill_page_cache_func(). > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> Much improved! But still some questions below... Thanx, Paul > --- > kernel/rcu/tree.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index cc34d13be181..9d9d3772cc45 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2908,6 +2908,8 @@ static inline bool > put_cached_bnode(struct kfree_rcu_cpu *krcp, > struct kvfree_rcu_bulk_data *bnode) > { > + if (atomic_read(&krcp->backoff_page_cache_fill)) > + return false; This will mean that under low-memory conditions, we will keep zero pages in ->bkvcache. All attempts to put something there will fail. This is probably not an issue for structures containing an rcu_head that are passed to kfree_rcu(p, field), but doesn't this mean that kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? This could seriously slow up freeing under low-memory conditions, which might exacerbate the low-memory conditions. Is this really what we want? Zero cached rather than just fewer cached? > // Check the limit. > if (krcp->nr_bkv_objs >= rcu_min_cached_objs) > return false; > @@ -3221,7 +3223,7 @@ static void fill_page_cache_func(struct work_struct *work) > int i; > > nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ? > - 1 : rcu_min_cached_objs; > + 0 : rcu_min_cached_objs; > > for (i = 0; i < nr_pages; i++) { I am still confused as to why we start "i" at zero rather than at ->nr_bkv_objs. What am I missing here? > bnode = (struct kvfree_rcu_bulk_data *) > -- > 2.32.0 >
> Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > executed before kfree_rcu_monitor() to drain page cache, if the bnode > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > page cache again in kfree_rcu_monitor(), this commit add a check > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > if the krcp structure's->backoff_page_cache_fill is set, prevent page > cache growing and disable allocated page in fill_page_cache_func(). > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > >Much improved! But still some questions below... > > Thanx, Paul > > --- > kernel/rcu/tree.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index cc34d13be181..9d9d3772cc45 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2908,6 +2908,8 @@ static inline bool > put_cached_bnode(struct kfree_rcu_cpu *krcp, > struct kvfree_rcu_bulk_data *bnode) > { > + if (atomic_read(&krcp->backoff_page_cache_fill)) > + return false; > >This will mean that under low-memory conditions, we will keep zero >pages in ->bkvcache. All attempts to put something there will fail. > >This is probably not an issue for structures containing an rcu_head >that are passed to kfree_rcu(p, field), but doesn't this mean that >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? >This could seriously slow up freeing under low-memory conditions, >which might exacerbate the low-memory conditions. Thanks for mentioning this, I didn't think of this before
On Tue, Apr 11, 2023 at 04:04:45AM +0000, Zhang, Qiang1 wrote: > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > page cache again in kfree_rcu_monitor(), this commit add a check > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > cache growing and disable allocated page in fill_page_cache_func(). > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > >Much improved! But still some questions below... > > > > Thanx, Paul > > > > --- > > kernel/rcu/tree.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index cc34d13be181..9d9d3772cc45 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2908,6 +2908,8 @@ static inline bool > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > struct kvfree_rcu_bulk_data *bnode) > > { > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > + return false; > > > >This will mean that under low-memory conditions, we will keep zero > >pages in ->bkvcache. All attempts to put something there will fail. > > > >This is probably not an issue for structures containing an rcu_head > >that are passed to kfree_rcu(p, field), but doesn't this mean that > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > >This could seriously slow up freeing under low-memory conditions, > >which might exacerbate the low-memory conditions. > > Thanks for mentioning this, I didn't think of this before
> > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > page cache again in kfree_rcu_monitor(), this commit add a check > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > cache growing and disable allocated page in fill_page_cache_func(). > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > >Much improved! But still some questions below... > > > > Thanx, Paul > > > > --- > > kernel/rcu/tree.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index cc34d13be181..9d9d3772cc45 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2908,6 +2908,8 @@ static inline bool > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > struct kvfree_rcu_bulk_data *bnode) > > { > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > + return false; > > > >This will mean that under low-memory conditions, we will keep zero > >pages in ->bkvcache. All attempts to put something there will fail. > > > >This is probably not an issue for structures containing an rcu_head > >that are passed to kfree_rcu(p, field), but doesn't this mean that > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > >This could seriously slow up freeing under low-memory conditions, > >which might exacerbate the low-memory conditions. > > Thanks for mentioning this, I didn't think of this before
On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > > page cache again in kfree_rcu_monitor(), this commit add a check > > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > > cache growing and disable allocated page in fill_page_cache_func(). > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > >Much improved! But still some questions below... > > > > > > Thanx, Paul > > > > > > --- > > > kernel/rcu/tree.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index cc34d13be181..9d9d3772cc45 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -2908,6 +2908,8 @@ static inline bool > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > struct kvfree_rcu_bulk_data *bnode) > > > { > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > + return false; > > > > > >This will mean that under low-memory conditions, we will keep zero > > >pages in ->bkvcache. All attempts to put something there will fail. > > > > > >This is probably not an issue for structures containing an rcu_head > > >that are passed to kfree_rcu(p, field), but doesn't this mean that > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > >This could seriously slow up freeing under low-memory conditions, > > >which might exacerbate the low-memory conditions. > > > > Thanks for mentioning this, I didn't think of this before
> > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > > page cache again in kfree_rcu_monitor(), this commit add a check > > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > > cache growing and disable allocated page in fill_page_cache_func(). > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > >Much improved! But still some questions below... > > > > > > Thanx, Paul > > > > > > --- > > > kernel/rcu/tree.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index cc34d13be181..9d9d3772cc45 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -2908,6 +2908,8 @@ static inline bool > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > struct kvfree_rcu_bulk_data *bnode) > > > { > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > + return false; > > > > > >This will mean that under low-memory conditions, we will keep zero > > >pages in ->bkvcache. All attempts to put something there will fail. > > > > > >This is probably not an issue for structures containing an rcu_head > > >that are passed to kfree_rcu(p, field), but doesn't this mean that > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > >This could seriously slow up freeing under low-memory conditions, > > >which might exacerbate the low-memory conditions. > > > > Thanks for mentioning this, I didn't think of this before
On Tue, Apr 11, 2023 at 03:09:13PM +0000, Zhang, Qiang1 wrote: > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > > > page cache again in kfree_rcu_monitor(), this commit add a check > > > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > > > cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > >Much improved! But still some questions below... > > > > > > > > Thanx, Paul > > > > > > > > --- > > > > kernel/rcu/tree.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > index cc34d13be181..9d9d3772cc45 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > struct kvfree_rcu_bulk_data *bnode) > > > > { > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > + return false; > > > > > > > >This will mean that under low-memory conditions, we will keep zero > > > >pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > >This is probably not an issue for structures containing an rcu_head > > > >that are passed to kfree_rcu(p, field), but doesn't this mean that > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > >This could seriously slow up freeing under low-memory conditions, > > > >which might exacerbate the low-memory conditions. > > > > > > Thanks for mentioning this, I didn't think of this before
On Tue, Apr 11, 2023 at 04:58:22PM +0200, Uladzislau Rezki wrote: > On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > > > page cache again in kfree_rcu_monitor(), this commit add a check > > > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > > > cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > >Much improved! But still some questions below... > > > > > > > > Thanx, Paul > > > > > > > > --- > > > > kernel/rcu/tree.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > index cc34d13be181..9d9d3772cc45 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > struct kvfree_rcu_bulk_data *bnode) > > > > { > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > + return false; > > > > > > > >This will mean that under low-memory conditions, we will keep zero > > > >pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > >This is probably not an issue for structures containing an rcu_head > > > >that are passed to kfree_rcu(p, field), but doesn't this mean that > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > >This could seriously slow up freeing under low-memory conditions, > > > >which might exacerbate the low-memory conditions. > > > > > > Thanks for mentioning this, I didn't think of this before
On Tue, Apr 11, 2023 at 09:42:37AM -0700, Paul E. McKenney wrote: > On Tue, Apr 11, 2023 at 04:58:22PM +0200, Uladzislau Rezki wrote: > > On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is > > > > > executed before kfree_rcu_monitor() to drain page cache, if the bnode > > > > > structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the > > > > > page cache again in kfree_rcu_monitor(), this commit add a check > > > > > for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), > > > > > if the krcp structure's->backoff_page_cache_fill is set, prevent page > > > > > cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > > > >Much improved! But still some questions below... > > > > > > > > > > Thanx, Paul > > > > > > > > > > --- > > > > > kernel/rcu/tree.c | 4 +++- > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > index cc34d13be181..9d9d3772cc45 100644 > > > > > --- a/kernel/rcu/tree.c > > > > > +++ b/kernel/rcu/tree.c > > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > > struct kvfree_rcu_bulk_data *bnode) > > > > > { > > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > > + return false; > > > > > > > > > >This will mean that under low-memory conditions, we will keep zero > > > > >pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > > > >This is probably not an issue for structures containing an rcu_head > > > > >that are passed to kfree_rcu(p, field), but doesn't this mean that > > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > > >This could seriously slow up freeing under low-memory conditions, > > > > >which might exacerbate the low-memory conditions. > > > > > > > > Thanks for mentioning this, I didn't think of this before
> On Tue, Apr 11, 2023 at 04:58:22PM +0200, Uladzislau Rezki wrote: > > On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() > > > > > is executed before kfree_rcu_monitor() to drain page cache, if > > > > > the bnode structure's->gp_snap has done, the kvfree_rcu_bulk() > > > > > will fill the page cache again in kfree_rcu_monitor(), this > > > > > commit add a check for krcp > > > > > structure's->backoff_page_cache_fill in put_cached_bnode(), if > > > > > the krcp structure's->backoff_page_cache_fill is set, prevent page cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > > > >Much improved! But still some questions below... > > > > > > > > > > Thanx, Paul > > > > > > > > > > --- > > > > > kernel/rcu/tree.c | 4 +++- > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index > > > > > cc34d13be181..9d9d3772cc45 100644 > > > > > --- a/kernel/rcu/tree.c > > > > > +++ b/kernel/rcu/tree.c > > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > > struct kvfree_rcu_bulk_data *bnode) { > > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > > + return false; > > > > > > > > > >This will mean that under low-memory conditions, we will keep > > > > >zero pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > > > >This is probably not an issue for structures containing an > > > > >rcu_head that are passed to kfree_rcu(p, field), but doesn't > > > > >this mean that > > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > > >This could seriously slow up freeing under low-memory > > > > >conditions, which might exacerbate the low-memory conditions. > > > > > > > > Thanks for mentioning this, I didn't think of this before
On Wed, Apr 12, 2023 at 09:14:15AM +0000, Zhang, Qiang1 wrote: > > > On Tue, Apr 11, 2023 at 04:58:22PM +0200, Uladzislau Rezki wrote: > > > On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() > > > > > > is executed before kfree_rcu_monitor() to drain page cache, if > > > > > > the bnode structure's->gp_snap has done, the kvfree_rcu_bulk() > > > > > > will fill the page cache again in kfree_rcu_monitor(), this > > > > > > commit add a check for krcp > > > > > > structure's->backoff_page_cache_fill in put_cached_bnode(), if > > > > > > the krcp structure's->backoff_page_cache_fill is set, prevent page cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > > > > > >Much improved! But still some questions below... > > > > > > > > > > > > Thanx, Paul > > > > > > > > > > > > --- > > > > > > kernel/rcu/tree.c | 4 +++- > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index > > > > > > cc34d13be181..9d9d3772cc45 100644 > > > > > > --- a/kernel/rcu/tree.c > > > > > > +++ b/kernel/rcu/tree.c > > > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > > > struct kvfree_rcu_bulk_data *bnode) { > > > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > > > + return false; > > > > > > > > > > > >This will mean that under low-memory conditions, we will keep > > > > > >zero pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > > > > > >This is probably not an issue for structures containing an > > > > > >rcu_head that are passed to kfree_rcu(p, field), but doesn't > > > > > >this mean that > > > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > > > >This could seriously slow up freeing under low-memory > > > > > >conditions, which might exacerbate the low-memory conditions. > > > > > > > > > > Thanks for mentioning this, I didn't think of this before
> > On Tue, Apr 11, 2023 at 04:58:22PM +0200, Uladzislau Rezki wrote: > > > On Tue, Apr 11, 2023 at 02:42:27PM +0000, Zhang, Qiang1 wrote: > > > > > > Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() > > > > > > is executed before kfree_rcu_monitor() to drain page cache, if > > > > > > the bnode structure's->gp_snap has done, the kvfree_rcu_bulk() > > > > > > will fill the page cache again in kfree_rcu_monitor(), this > > > > > > commit add a check for krcp > > > > > > structure's->backoff_page_cache_fill in put_cached_bnode(), if > > > > > > the krcp structure's->backoff_page_cache_fill is set, prevent page cache growing and disable allocated page in fill_page_cache_func(). > > > > > > > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > > > > > > > > >Much improved! But still some questions below... > > > > > > > > > > > > Thanx, Paul > > > > > > > > > > > > --- > > > > > > kernel/rcu/tree.c | 4 +++- > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index > > > > > > cc34d13be181..9d9d3772cc45 100644 > > > > > > --- a/kernel/rcu/tree.c > > > > > > +++ b/kernel/rcu/tree.c > > > > > > @@ -2908,6 +2908,8 @@ static inline bool > > > > > > put_cached_bnode(struct kfree_rcu_cpu *krcp, > > > > > > struct kvfree_rcu_bulk_data *bnode) { > > > > > > + if (atomic_read(&krcp->backoff_page_cache_fill)) > > > > > > + return false; > > > > > > > > > > > >This will mean that under low-memory conditions, we will keep > > > > > >zero pages in ->bkvcache. All attempts to put something there will fail. > > > > > > > > > > > >This is probably not an issue for structures containing an > > > > > >rcu_head that are passed to kfree_rcu(p, field), but doesn't > > > > > >this mean that > > > > > >kfree_rcu_mightsleep() unconditionally invokes synchronize_rcu()? > > > > > >This could seriously slow up freeing under low-memory > > > > > >conditions, which might exacerbate the low-memory conditions. > > > > > > > > > > Thanks for mentioning this, I didn't think of this before
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cc34d13be181..9d9d3772cc45 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2908,6 +2908,8 @@ static inline bool put_cached_bnode(struct kfree_rcu_cpu *krcp, struct kvfree_rcu_bulk_data *bnode) { + if (atomic_read(&krcp->backoff_page_cache_fill)) + return false; // Check the limit. if (krcp->nr_bkv_objs >= rcu_min_cached_objs) return false; @@ -3221,7 +3223,7 @@ static void fill_page_cache_func(struct work_struct *work) int i; nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ? - 1 : rcu_min_cached_objs; + 0 : rcu_min_cached_objs; for (i = 0; i < nr_pages; i++) { bnode = (struct kvfree_rcu_bulk_data *)
Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is executed before kfree_rcu_monitor() to drain page cache, if the bnode structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the page cache again in kfree_rcu_monitor(), this commit add a check for krcp structure's->backoff_page_cache_fill in put_cached_bnode(), if the krcp structure's->backoff_page_cache_fill is set, prevent page cache growing and disable allocated page in fill_page_cache_func(). Signed-off-by: Zqiang <qiang1.zhang@intel.com> --- kernel/rcu/tree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)