Re: [PATCHv2] mm: skip CMA pages when they are not available

[Zhaoyang Huang]

On Fri, Apr 21, 2023 at 2:47 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> "zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx> writes:
>
> > 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. There has been
> > commit(168676649) to fix it by trying CMA pages first instead of fallback in
> > rmqueue. I would like to propose another one from reclaiming perspective.
> >
> > 04166 < 4> [   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
> > 0419C < 4> [   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
> > 0419D < 4> [   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
> >       ......
> > 041EA < 4> [   36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC)
> > 041EB < 4> [   36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0
> > 041EC < 4> [   36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0
>
> From the above description, you are trying to resolve an issue that has
> been resolved already.  If so, why do we need your patch?  What is the
> issue it try to resolve in current upstream kernel?

Please consider this bellowing sequence as __perform_reclaim() return
with reclaiming 32 CMA pages successfully and then lead to
get_page_from_freelist failure if MIGRATE_CMA is NOT over 1/2 number
of free pages which will then unreserve H pageblocks and drain percpu
pageset. right? Furthermore, this could also introduce OOM as
direct_reclaim is the final guard for alloc_pages.

*did_some_progress = __perform_reclaim(gfp_mask, order, ac);

retry:
page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);

if (!page && !drained) {
unreserve_highatomic_pageblock(ac, false);
drain_all_pages(NULL);
drained = true;
goto retry;
}

return page;
>
> At the first glance, I don't think your patch doesn't make sense.  But
> you really need to show the value of the patch.
>
> Best Regards,
> Huang, Ying
>
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> > v2: update commit message and fix build error when CONFIG_CMA is not set
> > ---
> > ---
> >  mm/vmscan.c | 15 +++++++++++++--
> >  1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index bd6637f..19fb445 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2225,10 +2225,16 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
> >       unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
> >       unsigned long skipped = 0;
> >       unsigned long scan, total_scan, nr_pages;
> > +     bool cma_cap = true;
> > +     struct page *page;
> >       LIST_HEAD(folios_skipped);
> >
> >       total_scan = 0;
> >       scan = 0;
> > +     if ((IS_ENABLED(CONFIG_CMA)) && !current_is_kswapd()
> > +             && (gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE))
> > +             cma_cap = false;
> > +
> >       while (scan < nr_to_scan && !list_empty(src)) {
> >               struct list_head *move_to = src;
> >               struct folio *folio;
> > @@ -2239,12 +2245,17 @@ 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) {
> > +             page = &folio->page;
> > +
> > +             if ((folio_zonenum(folio) > sc->reclaim_idx)
> > +#ifdef CONFIG_CMA
> > +                     || (get_pageblock_migratetype(page) == MIGRATE_CMA && !cma_cap)
> > +#endif
> > +             ) {
> >                       nr_skipped[folio_zonenum(folio)] += nr_pages;
> >                       move_to = &folios_skipped;
> >                       goto move;
> >               }
> > -
> >               /*
> >                * Do not count skipped folios because that makes the function
> >                * return with no isolated folios if the LRU mostly contains