From: Alistair Popple <apopple@xxxxxxxxxx> Subject: mm/migrate.c: remove MIGRATE_PFN_LOCKED MIGRATE_PFN_LOCKED is used to indicate to migrate_vma_prepare() that a source page was already locked during migrate_vma_collect(). If it wasn't then the a second attempt is made to lock the page. However if the first attempt failed it's unlikely a second attempt will succeed, and the retry adds complexity. So clean this up by removing the retry and MIGRATE_PFN_LOCKED flag. Destination pages are also meant to have the MIGRATE_PFN_LOCKED flag set, but nothing actually checks that. Link: https://lkml.kernel.org/r/20211025041608.289017-1-apopple@xxxxxxxxxx Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx> Cc: Alex Deucher <alexander.deucher@xxxxxxx> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/vm/hmm.rst | 2 arch/powerpc/kvm/book3s_hv_uvmem.c | 4 drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 2 drivers/gpu/drm/nouveau/nouveau_dmem.c | 4 include/linux/migrate.h | 1 lib/test_hmm.c | 5 mm/migrate.c | 145 ++++----------------- 7 files changed, 35 insertions(+), 128 deletions(-) --- a/arch/powerpc/kvm/book3s_hv_uvmem.c~mm-migratec-remove-migrate_pfn_locked +++ a/arch/powerpc/kvm/book3s_hv_uvmem.c @@ -560,7 +560,7 @@ static int __kvmppc_svm_page_out(struct gpa, 0, page_shift); if (ret == U_SUCCESS) - *mig.dst = migrate_pfn(pfn) | MIGRATE_PFN_LOCKED; + *mig.dst = migrate_pfn(pfn); else { unlock_page(dpage); __free_page(dpage); @@ -774,7 +774,7 @@ static int kvmppc_svm_page_in(struct vm_ } } - *mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; + *mig.dst = migrate_pfn(page_to_pfn(dpage)); migrate_vma_pages(&mig); out_finalize: migrate_vma_finalize(&mig); --- a/Documentation/vm/hmm.rst~mm-migratec-remove-migrate_pfn_locked +++ a/Documentation/vm/hmm.rst @@ -360,7 +360,7 @@ between device driver specific code and system memory page, locks the page with ``lock_page()``, and fills in the ``dst`` array entry with:: - dst[i] = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; + dst[i] = migrate_pfn(page_to_pfn(dpage)); Now that the driver knows that this page is being migrated, it can invalidate device private MMU mappings and copy device private memory --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c~mm-migratec-remove-migrate_pfn_locked +++ a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c @@ -317,7 +317,6 @@ svm_migrate_copy_to_vram(struct amdgpu_d migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]); svm_migrate_get_vram_page(prange, migrate->dst[i]); migrate->dst[i] = migrate_pfn(migrate->dst[i]); - migrate->dst[i] |= MIGRATE_PFN_LOCKED; src[i] = dma_map_page(dev, spage, 0, PAGE_SIZE, DMA_TO_DEVICE); r = dma_mapping_error(dev, src[i]); @@ -610,7 +609,6 @@ svm_migrate_copy_to_ram(struct amdgpu_de dst[i] >> PAGE_SHIFT, page_to_pfn(dpage)); migrate->dst[i] = migrate_pfn(page_to_pfn(dpage)); - migrate->dst[i] |= MIGRATE_PFN_LOCKED; j++; } --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c~mm-migratec-remove-migrate_pfn_locked +++ a/drivers/gpu/drm/nouveau/nouveau_dmem.c @@ -166,7 +166,7 @@ static vm_fault_t nouveau_dmem_fault_cop goto error_dma_unmap; mutex_unlock(&svmm->mutex); - args->dst[0] = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; + args->dst[0] = migrate_pfn(page_to_pfn(dpage)); return 0; error_dma_unmap: @@ -602,7 +602,7 @@ static unsigned long nouveau_dmem_migrat ((paddr >> PAGE_SHIFT) << NVIF_VMM_PFNMAP_V0_ADDR_SHIFT); if (src & MIGRATE_PFN_WRITE) *pfn |= NVIF_VMM_PFNMAP_V0_W; - return migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; + return migrate_pfn(page_to_pfn(dpage)); out_dma_unmap: dma_unmap_page(dev, *dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL); --- a/include/linux/migrate.h~mm-migratec-remove-migrate_pfn_locked +++ a/include/linux/migrate.h @@ -110,7 +110,6 @@ static inline int migrate_misplaced_page */ #define MIGRATE_PFN_VALID (1UL << 0) #define MIGRATE_PFN_MIGRATE (1UL << 1) -#define MIGRATE_PFN_LOCKED (1UL << 2) #define MIGRATE_PFN_WRITE (1UL << 3) #define MIGRATE_PFN_SHIFT 6 --- a/lib/test_hmm.c~mm-migratec-remove-migrate_pfn_locked +++ a/lib/test_hmm.c @@ -613,8 +613,7 @@ static void dmirror_migrate_alloc_and_co */ rpage->zone_device_data = dmirror; - *dst = migrate_pfn(page_to_pfn(dpage)) | - MIGRATE_PFN_LOCKED; + *dst = migrate_pfn(page_to_pfn(dpage)); if ((*src & MIGRATE_PFN_WRITE) || (!spage && args->vma->vm_flags & VM_WRITE)) *dst |= MIGRATE_PFN_WRITE; @@ -1137,7 +1136,7 @@ static vm_fault_t dmirror_devmem_fault_a lock_page(dpage); xa_erase(&dmirror->pt, addr >> PAGE_SHIFT); copy_highpage(dpage, spage); - *dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; + *dst = migrate_pfn(page_to_pfn(dpage)); if (*src & MIGRATE_PFN_WRITE) *dst |= MIGRATE_PFN_WRITE; } --- a/mm/migrate.c~mm-migratec-remove-migrate_pfn_locked +++ a/mm/migrate.c @@ -2362,7 +2362,6 @@ again: * can't be dropped from it). */ get_page(page); - migrate->cpages++; /* * Optimize for the common case where page is only mapped once @@ -2372,7 +2371,7 @@ again: if (trylock_page(page)) { pte_t swp_pte; - mpfn |= MIGRATE_PFN_LOCKED; + migrate->cpages++; ptep_get_and_clear(mm, addr, ptep); /* Setup special migration page table entry */ @@ -2406,6 +2405,9 @@ again: if (pte_present(pte)) unmapped++; + } else { + put_page(page); + mpfn = 0; } next: @@ -2510,15 +2512,17 @@ static bool migrate_vma_check_page(struc } /* - * migrate_vma_prepare() - lock pages and isolate them from the lru + * migrate_vma_unmap() - replace page mapping with special migration pte entry * @migrate: migrate struct containing all migration information * - * This locks pages that have been collected by migrate_vma_collect(). Once each - * page is locked it is isolated from the lru (for non-device pages). Finally, - * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be - * migrated by concurrent kernel threads. + * Isolate pages from the LRU and replace mappings (CPU page table pte) with a + * special migration pte entry and check if it has been pinned. Pinned pages are + * restored because we cannot migrate them. + * + * This is the last step before we call the device driver callback to allocate + * destination memory and copy contents of original page over to new page. */ -static void migrate_vma_prepare(struct migrate_vma *migrate) +static void migrate_vma_unmap(struct migrate_vma *migrate) { const unsigned long npages = migrate->npages; const unsigned long start = migrate->start; @@ -2527,32 +2531,12 @@ static void migrate_vma_prepare(struct m lru_add_drain(); - for (i = 0; (i < npages) && migrate->cpages; i++) { + for (i = 0; i < npages; i++) { struct page *page = migrate_pfn_to_page(migrate->src[i]); - bool remap = true; if (!page) continue; - if (!(migrate->src[i] & MIGRATE_PFN_LOCKED)) { - /* - * Because we are migrating several pages there can be - * a deadlock between 2 concurrent migration where each - * are waiting on each other page lock. - * - * Make migrate_vma() a best effort thing and backoff - * for any page we can not lock right away. - */ - if (!trylock_page(page)) { - migrate->src[i] = 0; - migrate->cpages--; - put_page(page); - continue; - } - remap = false; - migrate->src[i] |= MIGRATE_PFN_LOCKED; - } - /* ZONE_DEVICE pages are not on LRU */ if (!is_zone_device_page(page)) { if (!PageLRU(page) && allow_drain) { @@ -2562,16 +2546,9 @@ static void migrate_vma_prepare(struct m } if (isolate_lru_page(page)) { - if (remap) { - migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; - migrate->cpages--; - restore++; - } else { - migrate->src[i] = 0; - unlock_page(page); - migrate->cpages--; - put_page(page); - } + migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; + migrate->cpages--; + restore++; continue; } @@ -2579,80 +2556,20 @@ static void migrate_vma_prepare(struct m put_page(page); } - if (!migrate_vma_check_page(page)) { - if (remap) { - migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; - migrate->cpages--; - restore++; - - if (!is_zone_device_page(page)) { - get_page(page); - putback_lru_page(page); - } - } else { - migrate->src[i] = 0; - unlock_page(page); - migrate->cpages--; + if (page_mapped(page)) + try_to_migrate(page, 0); - if (!is_zone_device_page(page)) - putback_lru_page(page); - else - put_page(page); + if (page_mapped(page) || !migrate_vma_check_page(page)) { + if (!is_zone_device_page(page)) { + get_page(page); + putback_lru_page(page); } - } - } - - for (i = 0, addr = start; i < npages && restore; i++, addr += PAGE_SIZE) { - struct page *page = migrate_pfn_to_page(migrate->src[i]); - if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE)) + migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; + migrate->cpages--; + restore++; continue; - - remove_migration_pte(page, migrate->vma, addr, page); - - migrate->src[i] = 0; - unlock_page(page); - put_page(page); - restore--; - } -} - -/* - * migrate_vma_unmap() - replace page mapping with special migration pte entry - * @migrate: migrate struct containing all migration information - * - * Replace page mapping (CPU page table pte) with a special migration pte entry - * and check again if it has been pinned. Pinned pages are restored because we - * cannot migrate them. - * - * This is the last step before we call the device driver callback to allocate - * destination memory and copy contents of original page over to new page. - */ -static void migrate_vma_unmap(struct migrate_vma *migrate) -{ - const unsigned long npages = migrate->npages; - const unsigned long start = migrate->start; - unsigned long addr, i, restore = 0; - - for (i = 0; i < npages; i++) { - struct page *page = migrate_pfn_to_page(migrate->src[i]); - - if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE)) - continue; - - if (page_mapped(page)) { - try_to_migrate(page, 0); - if (page_mapped(page)) - goto restore; } - - if (migrate_vma_check_page(page)) - continue; - -restore: - migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; - migrate->cpages--; - restore++; } for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) { @@ -2665,12 +2582,8 @@ restore: migrate->src[i] = 0; unlock_page(page); + put_page(page); restore--; - - if (is_zone_device_page(page)) - put_page(page); - else - putback_lru_page(page); } } @@ -2693,8 +2606,8 @@ restore: * it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE * flag set). Once these are allocated and copied, the caller must update each * corresponding entry in the dst array with the pfn value of the destination - * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_LOCKED flags set - * (destination pages must have their struct pages locked, via lock_page()). + * page and with MIGRATE_PFN_VALID. Destination pages must be locked via + * lock_page(). * * Note that the caller does not have to migrate all the pages that are marked * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from @@ -2764,8 +2677,6 @@ int migrate_vma_setup(struct migrate_vma migrate_vma_collect(args); if (args->cpages) - migrate_vma_prepare(args); - if (args->cpages) migrate_vma_unmap(args); /* _
