在 2024/12/17 14:31, Barry Song 写道:
On Tue, Dec 17, 2024 at 7:14 PM Barry Song <21cnbao@xxxxxxxxx> wrote: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 NUMAOther 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 hereDo 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 targetsI'm not sure if this document is correct for cases other than GUP.Hi yangge, Could we please run the same test using dma-buf? The simplest approach is to use system_heap from drivers/dma-buf/heaps/system_heap.c.
Ok, I'll try it.
Userspace programming it is quite straightforward: https://static.linaro.org/connect/lvc21/presentations/lvc21-120.pdf struct dma_heap_allocation_data heap_data = { .len = 1048576, // 1meg .fd_flags = O_RDWR | O_CLOEXEC, }; fd = open(“/dev/dma_heap/system”, O_RDONLY | O_CLOEXEC); if (fd < 0) return fd; ret = ioctl(fd, DMA_HEAP_IOCTL_ALLOC, &heap_data); There are two objectives: 1. Whether we should fix the changelog and code documentation, then send another version. 2. If there are issues elsewhere, we need to port the patch into the Android common kernel, which heavily uses dma-buf. Ok.*/ 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; /* -- 2.7.4Thanks Barry
