On 8/26/24 21:18, Michal Hocko wrote: > On Mon 26-08-24 18:49:23, Matthew Wilcox wrote: >> On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote: > [...] >> > If a plan revert is preferably, I will go with it. >> >> There aren't any other users of PF_MEMALLOC_NOWARN and it definitely >> seems like something you want at a callsite rather than blanket for every >> allocation below this point. We don't seem to have many PF_ flags left, >> so let's not keep it around if there's no immediate plans for it. > > Good point. What about this? > --- > From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxxx> > Date: Mon, 26 Aug 2024 21:15:02 +0200 > Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM, > PF_MEMALLOC_NOWARN" > > This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4. > > There is no existing user of those flags. PF_MEMALLOC_NOWARN is > dangerous because a nested allocation context can use GFP_NOFAIL which > could cause unexpected failure. Such a code would be hard to maintain > because it could be deeper in the call chain. > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > that such a allocation contex is inherently unsafe if the context > doesn't fully control all allocations called from this context. > > While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM > is it doesn't have any user and as Matthew has pointed out we are > running out of those flags so better reclaim it without any real users. > > [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/ > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx> > --- > include/linux/sched.h | 4 ++-- > include/linux/sched/mm.h | 17 ++++------------- > 2 files changed, 6 insertions(+), 15 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index f8d150343d42..731ff1078c9e 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1657,8 +1657,8 @@ extern struct pid *cad_pid; > * I am cleaning dirty pages from some other bdi. */ > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ > -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */ > -#define PF_MEMALLOC_NOWARN 0x01000000 /* All allocation requests will inherit __GFP_NOWARN */ > +#define PF__HOLE__00800000 0x00800000 > +#define PF__HOLE__01000000 0x01000000 > #define PF__HOLE__02000000 0x02000000 > #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */ > #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */ > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > index 91546493c43d..07c4fde32827 100644 > --- a/include/linux/sched/mm.h > +++ b/include/linux/sched/mm.h > @@ -258,25 +258,16 @@ static inline gfp_t current_gfp_context(gfp_t flags) > { > unsigned int pflags = READ_ONCE(current->flags); > > - if (unlikely(pflags & (PF_MEMALLOC_NOIO | > - PF_MEMALLOC_NOFS | > - PF_MEMALLOC_NORECLAIM | > - PF_MEMALLOC_NOWARN | > - PF_MEMALLOC_PIN))) { > + if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) { > /* > - * Stronger flags before weaker flags: > - * NORECLAIM implies NOIO, which in turn implies NOFS > + * NOIO implies both NOIO and NOFS and it is a weaker context > + * so always make sure it makes precedence > */ > - if (pflags & PF_MEMALLOC_NORECLAIM) > - flags &= ~__GFP_DIRECT_RECLAIM; > - else if (pflags & PF_MEMALLOC_NOIO) > + if (pflags & PF_MEMALLOC_NOIO) > flags &= ~(__GFP_IO | __GFP_FS); > else if (pflags & PF_MEMALLOC_NOFS) > flags &= ~__GFP_FS; > > - if (pflags & PF_MEMALLOC_NOWARN) > - flags |= __GFP_NOWARN; > - > if (pflags & PF_MEMALLOC_PIN) > flags &= ~__GFP_MOVABLE; > }
