On Tue, 12 May 2026 13:29:52 +0200
Oleg Nesterov <[email protected]> wrote:
> On 05/11, Rosen Penev wrote:
> >
> > struct xol_area {
> > wait_queue_head_t wq; /* if all slots are
> > busy */
> > - unsigned long *bitmap; /* 0 = free slot */
> >
> > struct page *page;
> > /*
> > @@ -117,6 +116,7 @@ struct xol_area {
> > * the vma go away, and we must handle that reasonably gracefully.
> > */
> > unsigned long vaddr; /* Page(s) of
> > instruction slots */
> > + unsigned long bitmap[]; /* 0 = free slot */
> > };
> >
> > static void uprobe_warn(struct task_struct *t, const char *msg)
> > @@ -1755,18 +1755,13 @@ static struct xol_area *__create_xol_area(unsigned
> > long vaddr)
> > struct xol_area *area;
> > void *insns;
> >
> > - area = kzalloc_obj(*area);
> > + area = kzalloc_flex(*area, bitmap, BITS_TO_LONGS(UINSNS_PER_PAGE));
>
> The downside is that kmalloc will use kmem_cache with ->object_size =
> PAGE_SIZE * 2,
> almost half of the allocated memory won't be used...
Hmm, is the bitmap so big?
#define UINSNS_PER_PAGE (PAGE_SIZE/UPROBE_XOL_SLOT_BYTES)
And even on arm64,
#define UPROBE_XOL_SLOT_BYTES AARCH64_INSN_SIZE
So if PAGE_SIZE is 4k, UINSNS_PER_PAGE is 1k, its BITS_TO_LONGS will
be 1024/64 = 16. So 128 bytes. So the object is allocated from
object_size = 256 ?
Thank you,
>
> But technically the patch looks correct so I won't argue.
>
> Oleg.
>
>
--
Masami Hiramatsu (Google) <[email protected]>
