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Message-ID: <CAGsJ_4ymXJOxTv8JKFVbzNMyfD52UdR6gwSWTdwUWV6ARGWfwQ@mail.gmail.com>
Date: Tue, 17 Dec 2024 21:49:40 +1300
From: Barry Song <21cnbao@...il.com>
To: Ge Yang <yangge1116@....com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org, david@...hat.com,
baolin.wang@...ux.alibaba.com, vbabka@...e.cz, liuzixing@...on.cn
Subject: Re: [PATCH V6] mm, compaction: don't use ALLOC_CMA in long term GUP flow
On Tue, Dec 17, 2024 at 8:12 PM Ge Yang <yangge1116@....com> wrote:
>
>
>
> 在 2024/12/17 14:14, Barry Song 写道:
> > On Tue, Dec 17, 2024 at 4:33 PM <yangge1116@....com> wrote:
> >>
> >> From: yangge <yangge1116@....com>
> >>
> >> 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.
Imagine we have only one NUMA node and no remote nodes to 'borrow'
memory from. What would happen as a result of this bug?
>
> >
> >> 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@...r.kernel.org>
> >> Signed-off-by: yangge <yangge1116@....com>
> >> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> >> ---
> >>
> >> 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
>
>
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