On Mon, Jul 26, 2021 at 12:05:44PM +0800, Chen Wandun wrote: > 在 2021/7/26 11:25, Matthew Wilcox 写道: > > On Mon, Jul 26, 2021 at 11:23:33AM +0800, Chen Wandun wrote: > > > struct page array can also be allocated in highmem during vmalloc, > > > that will ease the low memory stress in 32bit system. > > Huh? Where does it get kmapped in order to access it? (i misread your patch, apologies) > The struct page array contain numbers of pointer of struct page, it is used to save > > pages that allocated for vmalloc mapping in vmap_pages_range, it does't need to kmap. > > > The main idea of this patch is come from: > > https://lore.kernel.org/lkml/20170307141020.29107-1-mhocko@xxxxxxxxxx/ you've misunderstood that patch. think about it: static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot, unsigned int page_shift, int node) { const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO; (now nested_gfp has neither DMA nor DMA32 set) gfp_mask |= __GFP_NOWARN; if (!(gfp_mask & (GFP_DMA | GFP_DMA32))) gfp_mask |= __GFP_HIGHMEM; (we set HIGHMEM if DMA and DMA32 are both not set) area->pages = __vmalloc_node(array_size, 1, nested_gfp, node, area->caller); (we don't need to set HIGHMEM here because it will be set for us in the second call to __vmalloc_area_node)
