From: Ralph Campbell <rcampbell@xxxxxxxxxx> Subject: mm/migrate: optimize migrate_vma_setup() for holes Patch series "mm/migrate: optimize migrate_vma_setup() for holes". A simple optimization for migrate_vma_*() when the source vma is not an anonymous vma and a new test case to exercise it. This patch (of 2): When migrating system memory to device private memory, if the source address range is a valid VMA range and there is no memory or a zero page, the source PFN array is marked as valid but with no PFN. This lets the device driver allocate private memory and clear it, then insert the new device private struct page into the CPU's page tables when migrate_vma_pages() is called. migrate_vma_pages() only inserts the new page if the VMA is an anonymous range. There is no point in telling the device driver to allocate device private memory and then not migrate the page. Instead, mark the source PFN array entries as not migrating to avoid this overhead. [rcampbell@xxxxxxxxxx: v2] Link: http://lkml.kernel.org/r/20200710194840.7602-2-rcampbell@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200710194840.7602-1-rcampbell@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200709165711.26584-1-rcampbell@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200709165711.26584-2-rcampbell@xxxxxxxxxx Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx> Cc: "Bharata B Rao" <bharata@xxxxxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/migrate.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) --- a/mm/migrate.c~mm-migrate-optimize-migrate_vma_setup-for-holes +++ a/mm/migrate.c @@ -2168,6 +2168,16 @@ static int migrate_vma_collect_hole(unsi struct migrate_vma *migrate = walk->private; unsigned long addr; + /* Only allow populating anonymous memory. */ + if (!vma_is_anonymous(walk->vma)) { + for (addr = start; addr < end; addr += PAGE_SIZE) { + migrate->src[migrate->npages] = 0; + migrate->dst[migrate->npages] = 0; + migrate->npages++; + } + return 0; + } + for (addr = start; addr < end; addr += PAGE_SIZE) { migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE; migrate->dst[migrate->npages] = 0; @@ -2260,8 +2270,10 @@ again: pte = *ptep; if (pte_none(pte)) { - mpfn = MIGRATE_PFN_MIGRATE; - migrate->cpages++; + if (vma_is_anonymous(vma)) { + mpfn = MIGRATE_PFN_MIGRATE; + migrate->cpages++; + } goto next; } _
