Re: [PATCHv4] mm: skip CMA pages when they are not available

[Zhaoyang Huang]

On Sat, May 27, 2023 at 7:03 AM Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> On Mon, May 22, 2023 at 02:36:03PM +0800, zhaoyang.huang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> >
> > This patch fixes unproductive reclaiming of CMA pages by skipping them when they
> > are not available for current context. It is arise from bellowing OOM issue, which
> > caused by large proportion of MIGRATE_CMA pages among free pages.
> >
> > [   36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0
> > [   36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB
> > [   36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB
> > ...
> > [   36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC)
> > [   36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0
> > [   36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0
> >
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> > v2: update commit message and fix build error when CONFIG_CMA is not set
> > v3,v4: update code and comments
> > ---
> > ---
> >  mm/vmscan.c | 23 ++++++++++++++++++++++-
> >  1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index bd6637f..20facec 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2193,6 +2193,26 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec,
> >
> >  }
> >
> > +#ifdef CONFIG_CMA
> > +/*
> > + * It is waste of effort to scan and reclaim CMA pages if it is not available
> > + * for current allocation context
> > + */
> > +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> > +{
> > +     if (!current_is_kswapd() &&
>
> The function is called by isolate_lru_folios which is used by both background
> and direct reclaims at the same time. And sc->reclaim_idx below to filter
> unproductive reclaim out is used for both cases but why does the cma is considering
> only direct reclaim path?
Because kswapd's sc->gfp_mask = GFP_KERNEL which can not distinguish
this scenario
>
>
> > +                     gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE &&
> > +                     get_pageblock_migratetype(&folio->page) == MIGRATE_CMA)
> > +             return true;
> > +     return false;
> > +}
> > +#else
> > +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> > +{
> > +     return false;
> > +}
> > +#endif
> > +
> >  /*
> >   * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
> >   *
> > @@ -2239,7 +2259,8 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
> >               nr_pages = folio_nr_pages(folio);
> >               total_scan += nr_pages;
> >
> > -             if (folio_zonenum(folio) > sc->reclaim_idx) {
> > +             if (folio_zonenum(folio) > sc->reclaim_idx ||
> > +                             skip_cma(folio, sc)) {
> >                       nr_skipped[folio_zonenum(folio)] += nr_pages;
> >                       move_to = &folios_skipped;
> >                       goto move;
> > --
> > 1.9.1
> >