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    SubjectRe: [PATCH 4/6] mm: Replace PF_MEMALLOC_NOFS with memalloc_nofs
    On Thu 25-06-20 12:31:20, Matthew Wilcox wrote:
    > We're short on PF_* flags, so make memalloc_nofs its own bit where we
    > have plenty of space.
    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

    forgot to add
    Acked-by: Michal Hocko <mhocko@suse.com>

    > ---
    > fs/iomap/buffered-io.c | 2 +-
    > include/linux/sched.h | 2 +-
    > include/linux/sched/mm.h | 13 ++++++-------
    > 3 files changed, 8 insertions(+), 9 deletions(-)
    >
    > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
    > index bcfc288dba3f..87d66c13bf5c 100644
    > --- a/fs/iomap/buffered-io.c
    > +++ b/fs/iomap/buffered-io.c
    > @@ -1502,7 +1502,7 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
    > * Given that we do not allow direct reclaim to call us, we should
    > * never be called in a recursive filesystem reclaim context.
    > */
    > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
    > + if (WARN_ON_ONCE(current->memalloc_nofs))
    > goto redirty;
    >
    > /*
    > diff --git a/include/linux/sched.h b/include/linux/sched.h
    > index cf18a3d2bc4c..eaf36ae1fde2 100644
    > --- a/include/linux/sched.h
    > +++ b/include/linux/sched.h
    > @@ -802,6 +802,7 @@ struct task_struct {
    > unsigned in_memstall:1;
    > #endif
    > unsigned memalloc_noio:1;
    > + unsigned memalloc_nofs:1;
    >
    > unsigned long atomic_flags; /* Flags requiring atomic access. */
    >
    > @@ -1505,7 +1506,6 @@ extern struct pid *cad_pid;
    > #define PF_NOFREEZE 0x00008000 /* This thread should not be frozen */
    > #define PF_FROZEN 0x00010000 /* Frozen for system suspend */
    > #define PF_KSWAPD 0x00020000 /* I am kswapd */
    > -#define PF_MEMALLOC_NOFS 0x00040000 /* All allocation requests will inherit GFP_NOFS */
    > #define PF_LOCAL_THROTTLE 0x00100000 /* Throttle writes only against the bdi I write to,
    > * I am cleaning dirty pages from some other bdi. */
    > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */
    > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
    > index b0089eadc367..08bc9d0606a8 100644
    > --- a/include/linux/sched/mm.h
    > +++ b/include/linux/sched/mm.h
    > @@ -175,20 +175,19 @@ static inline bool in_vfork(struct task_struct *tsk)
    >
    > /*
    > * Applies per-task gfp context to the given allocation flags.
    > - * PF_MEMALLOC_NOFS implies GFP_NOFS
    > * PF_MEMALLOC_NOCMA implies no allocation from CMA region.
    > */
    > static inline gfp_t current_gfp_context(gfp_t flags)
    > {
    > - if (unlikely(current->flags & (PF_MEMALLOC_NOFS | PF_MEMALLOC_NOCMA) ||
    > - current->memalloc_noio)) {
    > + if (unlikely((current->flags & PF_MEMALLOC_NOCMA) ||
    > + current->memalloc_noio || current->memalloc_nofs)) {
    > /*
    > * NOIO implies both NOIO and NOFS and it is a weaker context
    > * so always make sure it makes precedence
    > */
    > if (current->memalloc_noio)
    > flags &= ~(__GFP_IO | __GFP_FS);
    > - else if (current->flags & PF_MEMALLOC_NOFS)
    > + else if (current->memalloc_nofs)
    > flags &= ~__GFP_FS;
    > #ifdef CONFIG_CMA
    > if (current->flags & PF_MEMALLOC_NOCMA)
    > @@ -254,8 +253,8 @@ static inline void memalloc_noio_restore(unsigned int flags)
    > */
    > static inline unsigned int memalloc_nofs_save(void)
    > {
    > - unsigned int flags = current->flags & PF_MEMALLOC_NOFS;
    > - current->flags |= PF_MEMALLOC_NOFS;
    > + unsigned int flags = current->memalloc_nofs;
    > + current->memalloc_nofs = 1;
    > return flags;
    > }
    >
    > @@ -269,7 +268,7 @@ static inline unsigned int memalloc_nofs_save(void)
    > */
    > static inline void memalloc_nofs_restore(unsigned int flags)
    > {
    > - current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags;
    > + current->memalloc_nofs = flags ? 1 : 0;
    > }
    >
    > static inline unsigned int memalloc_noreclaim_save(void)
    > --
    > 2.27.0

    --
    Michal Hocko
    SUSE Labs

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