| Message ID | 20200819022425.25188-2-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | avoid xfs transaction reservation recursion | expand |
On Wed, Aug 19, 2020 at 10:24:24AM +0800, Yafang Shao wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > Since XFS needs to pretend to be kswapd in some of its worker threads, > create methods to save & restore kswapd state. Don't bother restoring > kswapd state in kswapd -- the only time we reach this code is when we're > exiting and the task_struct is about to be destroyed anyway. > > Cc: Dave Chinner <david@fromorbit.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Michal Hocko <mhocko@kernel.org> > Cc: Darrick J. Wong <darrick.wong@oracle.com> > Cc: Matthew Wilcox <willy@infradead.org> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> See https://lore.kernel.org/linux-mm/20200625123143.GK1320@dhcp22.suse.cz/ Please add: Acked-by: Michal Hocko <mhocko@suse.com> > +/* > + * Tell the memory management that we're a "memory allocator", > + * and that if we need more memory we should get access to it > + * regardless (see "__alloc_pages()"). "kswapd" should > + * never get caught in the normal page freeing logic. > + * > + * (Kswapd normally doesn't need memory anyway, but sometimes > + * you need a small amount of memory in order to be able to > + * page out something else, and this flag essentially protects > + * us from recursively trying to free more memory as we're > + * trying to free the first piece of memory in the first place). > + */ And let's change that comment as suggested by Michal (slightly edited by me): /* * Tell the memory management code that this thread is working on behalf * of background memory reclaim (like kswapd). That means that it will * get access to memory reserves should it need to allocate memory in * order to make forward progress. With this great power comes great * responsibility to not exhaust those reserves. */ > +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) > + > +static inline unsigned long become_kswapd(void) > +{ > + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; > + > + current->flags |= KSWAPD_PF_FLAGS; > + > + return flags; > +} > + > +static inline void restore_kswapd(unsigned long flags) > +{ > + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); > +} > + > #ifdef CONFIG_MEMCG > /** > * memalloc_use_memcg - Starts the remote memcg charging scope. > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 99e1796eb833..3a2615bfde35 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3859,19 +3859,7 @@ static int kswapd(void *p) > if (!cpumask_empty(cpumask)) > set_cpus_allowed_ptr(tsk, cpumask); > > - /* > - * Tell the memory management that we're a "memory allocator", > - * and that if we need more memory we should get access to it > - * regardless (see "__alloc_pages()"). "kswapd" should > - * never get caught in the normal page freeing logic. > - * > - * (Kswapd normally doesn't need memory anyway, but sometimes > - * you need a small amount of memory in order to be able to > - * page out something else, and this flag essentially protects > - * us from recursively trying to free more memory as we're > - * trying to free the first piece of memory in the first place). > - */ > - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > + become_kswapd(); > set_freezable(); > > WRITE_ONCE(pgdat->kswapd_order, 0); > @@ -3921,8 +3909,6 @@ static int kswapd(void *p) > goto kswapd_try_sleep; > } > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > - > return 0; > } > > -- > 2.18.1 >
On Wed, Aug 19, 2020 at 11:08 AM Matthew Wilcox <willy@infradead.org> wrote: > > On Wed, Aug 19, 2020 at 10:24:24AM +0800, Yafang Shao wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > Since XFS needs to pretend to be kswapd in some of its worker threads, > > create methods to save & restore kswapd state. Don't bother restoring > > kswapd state in kswapd -- the only time we reach this code is when we're > > exiting and the task_struct is about to be destroyed anyway. > > > > Cc: Dave Chinner <david@fromorbit.com> > > Cc: Christoph Hellwig <hch@infradead.org> > > Cc: Michal Hocko <mhocko@kernel.org> > > Cc: Darrick J. Wong <darrick.wong@oracle.com> > > Cc: Matthew Wilcox <willy@infradead.org> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > > See https://lore.kernel.org/linux-mm/20200625123143.GK1320@dhcp22.suse.cz/ > > Please add: > > Acked-by: Michal Hocko <mhocko@suse.com> > Sure. I missed that discussion. > > +/* > > + * Tell the memory management that we're a "memory allocator", > > + * and that if we need more memory we should get access to it > > + * regardless (see "__alloc_pages()"). "kswapd" should > > + * never get caught in the normal page freeing logic. > > + * > > + * (Kswapd normally doesn't need memory anyway, but sometimes > > + * you need a small amount of memory in order to be able to > > + * page out something else, and this flag essentially protects > > + * us from recursively trying to free more memory as we're > > + * trying to free the first piece of memory in the first place). > > + */ > > And let's change that comment as suggested by Michal (slightly edited > by me): > > /* > * Tell the memory management code that this thread is working on behalf > * of background memory reclaim (like kswapd). That means that it will > * get access to memory reserves should it need to allocate memory in > * order to make forward progress. With this great power comes great > * responsibility to not exhaust those reserves. > */ > I will update it with that comment. > > +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) > > + > > +static inline unsigned long become_kswapd(void) > > +{ > > + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; > > + > > + current->flags |= KSWAPD_PF_FLAGS; > > + > > + return flags; > > +} > > + > > +static inline void restore_kswapd(unsigned long flags) > > +{ > > + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); > > +} > > + > > #ifdef CONFIG_MEMCG > > /** > > * memalloc_use_memcg - Starts the remote memcg charging scope. > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 99e1796eb833..3a2615bfde35 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -3859,19 +3859,7 @@ static int kswapd(void *p) > > if (!cpumask_empty(cpumask)) > > set_cpus_allowed_ptr(tsk, cpumask); > > > > - /* > > - * Tell the memory management that we're a "memory allocator", > > - * and that if we need more memory we should get access to it > > - * regardless (see "__alloc_pages()"). "kswapd" should > > - * never get caught in the normal page freeing logic. > > - * > > - * (Kswapd normally doesn't need memory anyway, but sometimes > > - * you need a small amount of memory in order to be able to > > - * page out something else, and this flag essentially protects > > - * us from recursively trying to free more memory as we're > > - * trying to free the first piece of memory in the first place). > > - */ > > - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > > + become_kswapd(); > > set_freezable(); > > > > WRITE_ONCE(pgdat->kswapd_order, 0); > > @@ -3921,8 +3909,6 @@ static int kswapd(void *p) > > goto kswapd_try_sleep; > > } > > > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > > - > > return 0; > > } > > > > -- > > 2.18.1 > >
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c index 2d25bab68764..a04a44238aab 100644 --- a/fs/xfs/libxfs/xfs_btree.c +++ b/fs/xfs/libxfs/xfs_btree.c @@ -2813,8 +2813,9 @@ xfs_btree_split_worker( { struct xfs_btree_split_args *args = container_of(work, struct xfs_btree_split_args, work); + bool is_kswapd = args->kswapd; unsigned long pflags; - unsigned long new_pflags = PF_MEMALLOC_NOFS; + int memalloc_nofs; /* * we are in a transaction context here, but may also be doing work @@ -2822,16 +2823,17 @@ xfs_btree_split_worker( * temporarily to ensure that we don't block waiting for memory reclaim * in any way. */ - if (args->kswapd) - new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; - - current_set_flags_nested(&pflags, new_pflags); + if (is_kswapd) + pflags = become_kswapd(); + memalloc_nofs = memalloc_nofs_save(); args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, args->key, args->curp, args->stat); complete(args->done); - current_restore_flags_nested(&pflags, new_pflags); + memalloc_nofs_restore(memalloc_nofs); + if (is_kswapd) + restore_kswapd(pflags); } /* diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index f889e332912f..80cc132f13a1 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -303,6 +303,34 @@ static inline void memalloc_nocma_restore(unsigned int flags) } #endif +/* + * Tell the memory management that we're a "memory allocator", + * and that if we need more memory we should get access to it + * regardless (see "__alloc_pages()"). "kswapd" should + * never get caught in the normal page freeing logic. + * + * (Kswapd normally doesn't need memory anyway, but sometimes + * you need a small amount of memory in order to be able to + * page out something else, and this flag essentially protects + * us from recursively trying to free more memory as we're + * trying to free the first piece of memory in the first place). + */ +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) + +static inline unsigned long become_kswapd(void) +{ + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; + + current->flags |= KSWAPD_PF_FLAGS; + + return flags; +} + +static inline void restore_kswapd(unsigned long flags) +{ + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); +} + #ifdef CONFIG_MEMCG /** * memalloc_use_memcg - Starts the remote memcg charging scope. diff --git a/mm/vmscan.c b/mm/vmscan.c index 99e1796eb833..3a2615bfde35 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3859,19 +3859,7 @@ static int kswapd(void *p) if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); - /* - * Tell the memory management that we're a "memory allocator", - * and that if we need more memory we should get access to it - * regardless (see "__alloc_pages()"). "kswapd" should - * never get caught in the normal page freeing logic. - * - * (Kswapd normally doesn't need memory anyway, but sometimes - * you need a small amount of memory in order to be able to - * page out something else, and this flag essentially protects - * us from recursively trying to free more memory as we're - * trying to free the first piece of memory in the first place). - */ - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; + become_kswapd(); set_freezable(); WRITE_ONCE(pgdat->kswapd_order, 0); @@ -3921,8 +3909,6 @@ static int kswapd(void *p) goto kswapd_try_sleep; } - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); - return 0; }