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Message-ID: <e6d3ef92-762a-414b-89ce-6f53f01f8df3@126.com>
Date: Tue, 17 Dec 2024 15:12:26 +0800
From: Ge Yang <yangge1116@....com>
To: Barry Song <21cnbao@...il.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
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.
>
>> 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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