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Message-ID: <CAGsJ_4xSbw7XDe1CWBAfYvMH35n0s1KaSze+wTUDOpwE-VrhfQ@mail.gmail.com>
Date: Tue, 17 Dec 2024 19:14:27 +1300
From: Barry Song <21cnbao@...il.com>
To: 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 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.
> 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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