Am Fri, 20 Mar 2015 17:25:29 +0200 schrieb Tomi Valkeinen <tomi.valkeinen@xxxxxx>: > On 20/03/15 16:47, Maxime Ripard wrote: > > On Fri, Mar 20, 2015 at 01:37:50PM +0200, Tomi Valkeinen wrote: > >> On 15/03/15 00:02, Geert Uytterhoeven wrote: > >>> On Fri, Mar 13, 2015 at 10:31 PM, Thomas Niederprüm > >>> <niederp@xxxxxxxxxxxxxxxx> wrote: > >>>> Am Tue, 10 Mar 2015 13:28:25 +0200 > >>>> schrieb Tomi Valkeinen <tomi.valkeinen@xxxxxx>: > >>>>> Also, isn't doing __pa() for the memory returned by vmalloc > >>>>> plain wrong? > >>>> > >>>>> What was the crash about when using kmalloc? It would be good > >>>>> to fix defio, as I don't see why it should not work with > >>>>> kmalloced memory. > >>>> > >>>> The main challenge here is that the memory handed to userspace > >>>> upon mmap call needs to be page aligned. The memory returned by > >>>> kmalloc has no such alignment, but the pointer presented to the > >>>> userspace program gets aligned to next page boundary. It's not > >>>> clear to me whether there is an easy way to obtain page aligned > >>>> kmalloc memory. Memory allocated by vmalloc on the other hand is > >>>> always aligned to page boundaries. This is why I chose to go for > >>>> vmalloc. > >>> > >>> __get_free_pages()? > >> > >> I'm not that experienced with mem management, so I have to ask... > >> __get_free_pages() probably works fine, but isn't vmalloc better > >> here? > >> > >> __get_free_pages() will give you possibly a lot more memory than > >> you need. And the memory is contiguous, so it could be difficult > >> to allocate a larger memory area. The driver doesn't need > >> contiguous memory (except in the virtual sense). > > > > vmalloc also returns pages, so the size will be page-aligned. It > > doesn't make much of a difference here, since we will only use a > > single page in both case (the max resolution of these screens is > > 128x39, with one bit per pixel). > > Ok, that's not much, then =). > > In that case __get_free_pages sounds fine. Even if the resolution > would be slightly higher, we're only talking about a page or two > extra. > > Usually double-underscore in front of a func means "don't call this". > I don't know why this one has the underscores. This irritated me as well. But since it turned out that there is even a section on "get_free_page and Friends" in LDD3 that talks about __get_free_pages() without any word of caution, I assumed it's ok to call this functions. Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
