Re: [PATCH V6] mm, compaction: don't use ALLOC_CMA in long term GUP flow

[Ge Yang <yangge1116@xxxxxxx>]

在 2024/12/17 14:14, Barry Song 写道:
> On Tue, Dec 17, 2024 at 4:33 PM <yangge1116@xxxxxxx> wrote:
> > From: yangge <yangge1116@xxxxxxx>
> >
> > Since commit 984fdba6a32e ("mm, compaction: use proper alloc_flags
> > in __compaction_suitable()") allow compaction to proceed when free
> > pages required for compaction reside in the CMA pageblocks, it's
> > possible that __compaction_suitable() always returns true, and in
> > some cases, it's not acceptable.
> >
> > There are 4 NUMA nodes on my machine, and each NUMA node has 32GB
> > of memory. I have configured 16GB of CMA memory on each NUMA node,
> > and starting a 32GB virtual machine with device passthrough is
> > extremely slow, taking almost an hour.
> >
> > During the start-up of the virtual machine, it will call
> > pin_user_pages_remote(..., FOLL_LONGTERM, ...) to allocate memory.
> > Long term GUP cannot allocate memory from CMA area, so a maximum
> > of 16 GB of no-CMA memory on a NUMA node can be used as virtual
> > machine memory. Since there is 16G of free CMA memory on the NUMA
>
> Other unmovable allocations, like dma_buf, which can be large in a
> Linux system, are
> also unable to allocate memory from CMA. My question is whether the issue you
> described applies to these allocations as well.
pin_user_pages_remote(..., FOLL_LONGTERM, ...) first attemps to allocate 
THP only on local node, and then fall back to remote NUMA nodes if the 
local allocation fail. For detail, see alloc_pages_mpol().

static struct page *alloc_pages_mpol()
{
    page = __alloc_frozen_pages_noprof(__GFP_THISNODE,...); // 1, try 
to allocate THP only on local node

    if (page || !(gpf & __GFP_DIRECT_RECLAIM))
        return page;

    page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask);//2, 
fall back to remote NUMA nodes
}

If dma_buf also uses the same way to allocate memory，dma_buf will also 
have this problem.

> > node, watermark for order-0 always be met for compaction, so
> > __compaction_suitable() always returns true, even if the node is
> > unable to allocate non-CMA memory for the virtual machine.
> >
> > For costly allocations, because __compaction_suitable() always
> > returns true, __alloc_pages_slowpath() can't exit at the appropriate
> > place, resulting in excessively long virtual machine startup times.
> > Call trace:
> > __alloc_pages_slowpath
> >      if (compact_result == COMPACT_SKIPPED ||
> >          compact_result == COMPACT_DEFERRED)
> >          goto nopage; // should exit __alloc_pages_slowpath() from here
>
> Do we face the same issue if we allocate dma-buf while CMA has plenty
> of free memory, but non-CMA has none?
>
> > In order to quickly fall back to remote node, we should remove
> > ALLOC_CMA both in __compaction_suitable() and __isolate_free_page()
> > in long term GUP flow. After this fix, starting a 32GB virtual machine
> > with device passthrough takes only a few seconds.
> >
> > Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: yangge <yangge1116@xxxxxxx>
> > Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >
> > V6:
> > -- update cc->alloc_flags to keep the original loginc
> >
> > V5:
> > - add 'alloc_flags' parameter for __isolate_free_page()
> > - remove 'usa_cma' variable
> >
> > V4:
> > - rich the commit log description
> >
> > V3:
> > - fix build errors
> > - add ALLOC_CMA both in should_continue_reclaim() and compaction_ready()
> >
> > V2:
> > - using the 'cc->alloc_flags' to determin if 'ALLOC_CMA' is needed
> > - rich the commit log description
> >
> >   include/linux/compaction.h |  6 ++++--
> >   mm/compaction.c            | 26 +++++++++++++++-----------
> >   mm/internal.h              |  3 ++-
> >   mm/page_alloc.c            |  7 +++++--
> >   mm/page_isolation.c        |  3 ++-
> >   mm/page_reporting.c        |  2 +-
> >   mm/vmscan.c                |  4 ++--
> >   7 files changed, 31 insertions(+), 20 deletions(-)
> >
> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> > index e947764..b4c3ac3 100644
> > --- a/include/linux/compaction.h
> > +++ b/include/linux/compaction.h
> > @@ -90,7 +90,8 @@ extern enum compact_result try_to_compact_pages(gfp_t gfp_mask,
> >                  struct page **page);
> >   extern void reset_isolation_suitable(pg_data_t *pgdat);
> >   extern bool compaction_suitable(struct zone *zone, int order,
> > -                                              int highest_zoneidx);
> > +                                              int highest_zoneidx,
> > +                                              unsigned int alloc_flags);
> >
> >   extern void compaction_defer_reset(struct zone *zone, int order,
> >                                  bool alloc_success);
> > @@ -108,7 +109,8 @@ static inline void reset_isolation_suitable(pg_data_t *pgdat)
> >   }
> >
> >   static inline bool compaction_suitable(struct zone *zone, int order,
> > -                                                     int highest_zoneidx)
> > +                                                     int highest_zoneidx,
> > +                                                     unsigned int alloc_flags)
> >   {
> >          return false;
> >   }
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 07bd227..d92ba6c 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -655,7 +655,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> >
> >                  /* Found a free page, will break it into order-0 pages */
> >                  order = buddy_order(page);
> > -               isolated = __isolate_free_page(page, order);
> > +               isolated = __isolate_free_page(page, order, cc->alloc_flags);
> >                  if (!isolated)
> >                          break;
> >                  set_page_private(page, order);
> > @@ -1634,7 +1634,7 @@ static void fast_isolate_freepages(struct compact_control *cc)
> >
> >                  /* Isolate the page if available */
> >                  if (page) {
> > -                       if (__isolate_free_page(page, order)) {
> > +                       if (__isolate_free_page(page, order, cc->alloc_flags)) {
> >                                  set_page_private(page, order);
> >                                  nr_isolated = 1 << order;
> >                                  nr_scanned += nr_isolated - 1;
> > @@ -2381,6 +2381,7 @@ static enum compact_result compact_finished(struct compact_control *cc)
> >
> >   static bool __compaction_suitable(struct zone *zone, int order,
> >                                    int highest_zoneidx,
> > +                                 unsigned int alloc_flags,
> >                                    unsigned long wmark_target)
> >   {
> >          unsigned long watermark;
> > @@ -2395,25 +2396,26 @@ static bool __compaction_suitable(struct zone *zone, int order,
> >           * even if compaction succeeds.
> >           * For costly orders, we require low watermark instead of min for
> >           * compaction to proceed to increase its chances.
> > -        * ALLOC_CMA is used, as pages in CMA pageblocks are considered
> > -        * suitable migration targets
> > +        * In addition to long term GUP flow, ALLOC_CMA is used, as pages in
> > +        * CMA pageblocks are considered suitable migration targets
>
> I'm not sure if this document is correct for cases other than GUP.
>
> >           */
> >          watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
> >                                  low_wmark_pages(zone) : min_wmark_pages(zone);
> >          watermark += compact_gap(order);
> >          return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
> > -                                  ALLOC_CMA, wmark_target);
> > +                                  alloc_flags & ALLOC_CMA, wmark_target);
> >   }
> >
> >   /*
> >    * compaction_suitable: Is this suitable to run compaction on this zone now?
> >    */
> > -bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx)
> > +bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx,
> > +                                  unsigned int alloc_flags)
> >   {
> >          enum compact_result compact_result;
> >          bool suitable;
> >
> > -       suitable = __compaction_suitable(zone, order, highest_zoneidx,
> > +       suitable = __compaction_suitable(zone, order, highest_zoneidx, alloc_flags,
> >                                           zone_page_state(zone, NR_FREE_PAGES));
> >          /*
> >           * fragmentation index determines if allocation failures are due to
> > @@ -2474,7 +2476,7 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
> >                  available = zone_reclaimable_pages(zone) / order;
> >                  available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> >                  if (__compaction_suitable(zone, order, ac->highest_zoneidx,
> > -                                         available))
> > +                                         alloc_flags, available))
> >                          return true;
> >          }
> >
> > @@ -2499,7 +2501,7 @@ compaction_suit_allocation_order(struct zone *zone, unsigned int order,
> >                                alloc_flags))
> >                  return COMPACT_SUCCESS;
> >
> > -       if (!compaction_suitable(zone, order, highest_zoneidx))
> > +       if (!compaction_suitable(zone, order, highest_zoneidx, alloc_flags))
> >                  return COMPACT_SKIPPED;
> >
> >          return COMPACT_CONTINUE;
> > @@ -2893,6 +2895,7 @@ static int compact_node(pg_data_t *pgdat, bool proactive)
> >          struct compact_control cc = {
> >                  .order = -1,
> >                  .mode = proactive ? MIGRATE_SYNC_LIGHT : MIGRATE_SYNC,
> > +               .alloc_flags = ALLOC_CMA,
> >                  .ignore_skip_hint = true,
> >                  .whole_zone = true,
> >                  .gfp_mask = GFP_KERNEL,
> > @@ -3037,7 +3040,7 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
> >
> >                  ret = compaction_suit_allocation_order(zone,
> >                                  pgdat->kcompactd_max_order,
> > -                               highest_zoneidx, ALLOC_WMARK_MIN);
> > +                               highest_zoneidx, ALLOC_CMA | ALLOC_WMARK_MIN);
> >                  if (ret == COMPACT_CONTINUE)
> >                          return true;
> >          }
> > @@ -3058,6 +3061,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
> >                  .search_order = pgdat->kcompactd_max_order,
> >                  .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
> >                  .mode = MIGRATE_SYNC_LIGHT,
> > +               .alloc_flags = ALLOC_CMA | ALLOC_WMARK_MIN,
> >                  .ignore_skip_hint = false,
> >                  .gfp_mask = GFP_KERNEL,
> >          };
> > @@ -3078,7 +3082,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
> >                          continue;
> >
> >                  ret = compaction_suit_allocation_order(zone,
> > -                               cc.order, zoneid, ALLOC_WMARK_MIN);
> > +                               cc.order, zoneid, cc.alloc_flags);
> >                  if (ret != COMPACT_CONTINUE)
> >                          continue;
> >
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 3922788..6d257c8 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -662,7 +662,8 @@ static inline void clear_zone_contiguous(struct zone *zone)
> >          zone->contiguous = false;
> >   }
> >
> > -extern int __isolate_free_page(struct page *page, unsigned int order);
> > +extern int __isolate_free_page(struct page *page, unsigned int order,
> > +                                   unsigned int alloc_flags);
> >   extern void __putback_isolated_page(struct page *page, unsigned int order,
> >                                      int mt);
> >   extern void memblock_free_pages(struct page *page, unsigned long pfn,
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index dde19db..1bfdca3 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2809,7 +2809,8 @@ void split_page(struct page *page, unsigned int order)
> >   }
> >   EXPORT_SYMBOL_GPL(split_page);
> >
> > -int __isolate_free_page(struct page *page, unsigned int order)
> > +int __isolate_free_page(struct page *page, unsigned int order,
> > +                                  unsigned int alloc_flags)
> >   {
> >          struct zone *zone = page_zone(page);
> >          int mt = get_pageblock_migratetype(page);
> > @@ -2823,7 +2824,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
> >                   * exists.
> >                   */
> >                  watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
> > -               if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
> > +               if (!zone_watermark_ok(zone, 0, watermark, 0,
> > +                           alloc_flags & ALLOC_CMA))
> >                          return 0;
> >          }
> >
> > @@ -6454,6 +6456,7 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
> >                  .order = -1,
> >                  .zone = page_zone(pfn_to_page(start)),
> >                  .mode = MIGRATE_SYNC,
> > +               .alloc_flags = ALLOC_CMA,
> >                  .ignore_skip_hint = true,
> >                  .no_set_skip_hint = true,
> >                  .alloc_contig = true,
> > diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> > index c608e9d..a1f2c79 100644
> > --- a/mm/page_isolation.c
> > +++ b/mm/page_isolation.c
> > @@ -229,7 +229,8 @@ static void unset_migratetype_isolate(struct page *page, int migratetype)
> >                          buddy = find_buddy_page_pfn(page, page_to_pfn(page),
> >                                                      order, NULL);
> >                          if (buddy && !is_migrate_isolate_page(buddy)) {
> > -                               isolated_page = !!__isolate_free_page(page, order);
> > +                               isolated_page = !!__isolate_free_page(page, order,
> > +                                                   ALLOC_CMA);
> >                                  /*
> >                                   * Isolating a free page in an isolated pageblock
> >                                   * is expected to always work as watermarks don't
> > diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> > index e4c428e..fd3813b 100644
> > --- a/mm/page_reporting.c
> > +++ b/mm/page_reporting.c
> > @@ -198,7 +198,7 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> >
> >                  /* Attempt to pull page from list and place in scatterlist */
> >                  if (*offset) {
> > -                       if (!__isolate_free_page(page, order)) {
> > +                       if (!__isolate_free_page(page, order, ALLOC_CMA)) {
> >                                  next = page;
> >                                  break;
> >                          }
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 5e03a61..33f5b46 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -5815,7 +5815,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
> >                                        sc->reclaim_idx, 0))
> >                          return false;
> >
> > -               if (compaction_suitable(zone, sc->order, sc->reclaim_idx))
> > +               if (compaction_suitable(zone, sc->order, sc->reclaim_idx, ALLOC_CMA))
> >                          return false;
> >          }
> >
> > @@ -6043,7 +6043,7 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> >                  return true;
> >
> >          /* Compaction cannot yet proceed. Do reclaim. */
> > -       if (!compaction_suitable(zone, sc->order, sc->reclaim_idx))
> > +       if (!compaction_suitable(zone, sc->order, sc->reclaim_idx, ALLOC_CMA))
> >                  return false;
> >
> >          /*
> > --
> > 2.7.4
>
> Thanks
> Barry