On Wed, Nov 4, 2020 at 8:30 AM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote:
>
> On Wed, Nov 04, 2020 at 10:17:16PM +0800, Yafang Shao wrote:
> > On Wed, Nov 4, 2020 at 3:48 AM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote:
> > >
> > > On Tue, Nov 03, 2020 at 09:17:53PM +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>
> > > > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > > > Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > > > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > > > ---
> > > > fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------
> > > > include/linux/sched/mm.h | 23 +++++++++++++++++++++++
> > > > mm/vmscan.c | 16 +---------------
> > > > 3 files changed, 32 insertions(+), 21 deletions(-)
> > > >
> > > > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> > > > index 2d25bab..a04a442 100644
> > > > --- a/fs/xfs/libxfs/xfs_btree.c
> > > > +++ b/fs/xfs/libxfs/xfs_btree.c
> > > > @@ -2813,8 +2813,9 @@ struct xfs_btree_split_args {
> > > > {
> > > > 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 @@ struct xfs_btree_split_args {
> > > > * 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);
> > >
> > > Note that there's a trivial merge conflict with the mrlock_t removal
> > > series. I'll carry the fix in the tree, assuming that everything
> > > passes.
> > >
> >
> > This patchset is based on Andrew's tree currently.
> > Seems I should rebase this patchset on your tree instead of Andrew's tree ?
>
> That depends on whether or not you want me to push these two patches
> through the xfs tree or if they're going through Andrew (Morton?)'s
> quiltset.
I think they could go through either, but the XFS tree might be ever-so-slightly
better.
>
> Frankly I'd rather take them via xfs since most of the diff is xfs...
Yeah, it's an XFS patch so let's throw it through the XFS tree.
>
> --D
>
> > > --D
> > >
> > > > }
> > > >
> > > > /*
> > > > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > > > index d5ece7a..2faf03e 100644
> > > > --- a/include/linux/sched/mm.h
> > > > +++ b/include/linux/sched/mm.h
> > > > @@ -278,6 +278,29 @@ static inline void memalloc_nocma_restore(unsigned int flags)
> > > > }
> > > > #endif
> > > >
> > > > +/*
> > > > + * 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
> > > > DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg);
> > > > /**
> > > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > > index 1b8f0e0..77bc1dd 100644
> > > > --- a/mm/vmscan.c
> > > > +++ b/mm/vmscan.c
> > > > @@ -3869,19 +3869,7 @@ 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);
> > > > @@ -3931,8 +3919,6 @@ static int kswapd(void *p)
> > > > goto kswapd_try_sleep;
> > > > }
> > > >
> > > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
> > > > -
> > > > return 0;
> > > > }
> > > >
> > > > --
> > > > 1.8.3.1
> > > >
> >
> >
> >
> > --
> > Thanks
> > Yafang
Best regards,
Amy Parker
(they/them)
