On Wed, Jan 11, 2023 at 04:02:26PM +0000, Al Viro wrote:
> On Wed, Jan 11, 2023 at 09:13:40AM -0500, Jeff Moyer wrote:
> > Hi, Al,
> >
> > Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes:
> >
> > > On Mon, Jan 09, 2023 at 06:56:29PM +0100, Fabio M. De Francesco wrote:
> > >
> > >> - ring = kmap_atomic(ctx->ring_pages[0]);
> > >> + ring = kmap_local_page(ctx->ring_pages[0]);
> > >> ring->nr = nr_events; /* user copy */
> > >> ring->id = ~0U;
> > >> ring->head = ring->tail = 0;
> > >> @@ -575,7 +575,7 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
> > >> ring->compat_features = AIO_RING_COMPAT_FEATURES;
> > >> ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
> > >> ring->header_length = sizeof(struct aio_ring);
> > >> - kunmap_atomic(ring);
> > >> + kunmap_local(ring);
> > >> flush_dcache_page(ctx->ring_pages[0]);
> > >
> > > I wonder if it would be more readable as memcpy_to_page(), actually...
> >
> > I'm not sure I understand what you're suggesting.
>
> memcpy_to_page(ctx->ring_pages[0], 0, &(struct aio_ring){
> .nr = nr_events, .id = ~0U, .magic = AIO_RING_MAGIC,
> .compat_features = AIO_RING_COMPAT_FEATURES,
> .in_compat_features = AIO_RING_INCOMPAT_FEATURES,
> .header_length = sizeof(struct aio_ring)},
> sizeof(struct aio_ring));
>
> instead of the lines from kmap_atomic to flush_dcache_page...
For us mere mortals I think this may parse easier as:
struct aio_ring r;
...
r = (struct aio_ring) {
.nr = nr_events,
.id = ~0U,
.magic = AIO_RING_MAGIC,
.compat_features = AIO_RING_COMPAT_FEATURES,
.incompat_features = AIO_RING_INCOMPAT_FEATURES,
.header_length = sizeof(struct aio_ring),
};
memcpy_to_page(ctx->ring_pages[0], 0, &r, sizeof(r));
...
Is there any concern with the extra assignments to the stack only to copy into
the page? I guess this is not a critical path?
Ira
> >
> > >>
> > >> return 0;
> > >> @@ -678,9 +678,9 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
> > >> * we are protected from page migration
> > >> * changes ring_pages by ->ring_lock.
> > >> */
> > >> - ring = kmap_atomic(ctx->ring_pages[0]);
> > >> + ring = kmap_local_page(ctx->ring_pages[0]);
> > >> ring->id = ctx->id;
> > >> - kunmap_atomic(ring);
> > >> + kunmap_local(ring);
> > >
> > > Incidentally, does it need flush_dcache_page()?
> >
> > Yes, good catch.
