On Wed, Aug 19, 2020 at 10:24:24AM +0800, Yafang Shao wrote: > From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> > > 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@xxxxxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> See https://lore.kernel.org/linux-mm/20200625123143.GK1320@xxxxxxxxxxxxxx/ Please add: Acked-by: Michal Hocko <mhocko@xxxxxxxx> > +/* > + * 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 >
