Hello Gioh, On Mon, Mar 10, 2014 at 7:16 PM, Gioh Kim <gioh.kim@xxxxxxx> wrote: > > The vm_map_ram has fragment problem because it couldn't > purge a chunk(ie, 4M address space) if there is a pinning object in > that addresss space. So it could consume all VMALLOC address space > easily. > We can fix the fragmentation problem with using vmap instead of vm_map_ram > but vmap is known to slow operation compared to vm_map_ram. Minchan said > vm_map_ram is 5 times faster than vmap in his experiment. So I thought > we should fix fragment problem of vm_map_ram because our proprietary > GPU driver has used it heavily. > > On second thought, it's not an easy because we should reuse freed > space for solving the problem and it could make more IPI and bitmap operation > for searching hole. It could mitigate API's goal which is very fast mapping. > And even fragmentation problem wouldn't show in 64 bit machine. > > Another option is that the user should separate long-life and short-life > object and use vmap for long-life but vm_map_ram for short-life. > If we inform the user about the characteristic of vm_map_ram > the user can choose one according to the page lifetime. > > Let's add some notice messages to user. > > Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx> > Reviewed-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> > --- > mm/vmalloc.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 0fdf968..85b6687 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1083,6 +1083,12 @@ EXPORT_SYMBOL(vm_unmap_ram); > * @node: prefer to allocate data structures on this node > * @prot: memory protection to use. PAGE_KERNEL for regular RAM > * > + * If you use this function for below VMAP_MAX_ALLOC pages, it could be faster > + * than vmap so it's good. But if you mix long-life and short-life object > + * with vm_map_ram, it could consume lots of address space by fragmentation > + * (expecially, 32bit machine). You could see failure in the end. looks like trivial typo. Shouldn't s/expecially/especially/ ? Thanks. > + * Please use this function for short-life object. > + * > * Returns: a pointer to the address that has been mapped, or %NULL on failure > */ > void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t prot) > -- > 1.7.9.5 > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a hrefmailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>