Step 2 Was: more strict KPI for vm_pager_get_pages()
Konstantin Belousov
kostikbel at gmail.com
Wed Jun 17 13:45:46 UTC 2015
On Wed, Jun 17, 2015 at 01:14:45PM +0300, Gleb Smirnoff wrote:
> Hi!
>
> On Tue, Jun 16, 2015 at 12:29:31AM +0300, Gleb Smirnoff wrote:
> T> This is step 2 of the "more strict pager KPI" patch:
> T>
> T> o Uninline vm_pager_get_pages() into vm_pager.c.
> T> o Keep all KASSERTs that enforce the KPI of pagers and of their
> T> consumers in one place: vm_pager_get_pages().
> T> o Keep the code that zeroes out partially valid pages in one
> T> place in vm_pager_get_pages().
>
> As Konstantin pointed out, it is very likely that right now NFS and SMD
> do the zeroing of partially valid pages incorrecrtly. So this code
> is removed from the generic vm_pager_get_pages() and this reduces
> step 2 patch to a very small change:
>
> o Uninline vm_pager_get_pages() into vm_pager.c.
> o Keep all KASSERTs that enforce the KPI of pagers and of their
> consumers in one place: vm_pager_get_pages().
> o Remove some KASSERTs from pagers that are already there in
> vm_pager_get_pages().
>
> Patch attached.
>
> --
> Totus tuus, Glebius.
> Index: sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
> ===================================================================
> --- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c (revision 284504)
> +++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c (working copy)
> @@ -5734,8 +5734,6 @@ zfs_getpages(struct vnode *vp, vm_page_t *m, int c
> object = mreq->object;
> error = 0;
>
> - KASSERT(vp->v_object == object, ("mismatching object"));
> -
> if (pcount > 1 && zp->z_blksz > PAGESIZE) {
> startoff = rounddown(IDX_TO_OFF(mreq->pindex), zp->z_blksz);
> reqstart = OFF_TO_IDX(round_page(startoff));
> Index: sys/fs/nfsclient/nfs_clbio.c
> ===================================================================
> --- sys/fs/nfsclient/nfs_clbio.c (revision 284504)
> +++ sys/fs/nfsclient/nfs_clbio.c (working copy)
> @@ -129,12 +129,6 @@ ncl_getpages(struct vop_getpages_args *ap)
> npages = btoc(count);
>
> /*
> - * Since the caller has busied the requested page, that page's valid
> - * field will not be changed by other threads.
> - */
> - vm_page_assert_xbusied(pages[ap->a_reqpage]);
> -
> - /*
> * If the requested page is partially valid, just return it and
> * allow the pager to zero-out the blanks. Partially valid pages
> * can only occur at the file EOF.
> Index: sys/vm/swap_pager.c
> ===================================================================
> --- sys/vm/swap_pager.c (revision 284504)
> +++ sys/vm/swap_pager.c (working copy)
> @@ -1118,10 +1118,6 @@ swap_pager_getpages(vm_object_t object, vm_page_t
>
> mreq = m[reqpage];
>
> - KASSERT(mreq->object == object,
> - ("swap_pager_getpages: object mismatch %p/%p",
> - object, mreq->object));
> -
> /*
> * Calculate range to retrieve. The pages have already been assigned
> * their swapblks. We require a *contiguous* range but we know it to
> Index: sys/vm/vm_pager.c
> ===================================================================
> --- sys/vm/vm_pager.c (revision 284504)
> +++ sys/vm/vm_pager.c (working copy)
> @@ -251,7 +251,88 @@ vm_pager_deallocate(object)
> }
>
> /*
> - * vm_pager_get_pages() - inline, see vm/vm_pager.h
> + * Retrieve pages from the VM system in order to map them into an object
> + * ( or into VM space somewhere ). If the pagein was successful, we
> + * must fully validate it.
> + */
> +int
> +vm_pager_get_pages(vm_object_t object, vm_page_t *m, int count, int reqpage)
> +{
> + int r;
> +
> + VM_OBJECT_ASSERT_WLOCKED(object);
> + KASSERT(count > 0, ("%s: 0 count", __func__));
> +
> +#ifdef INVARIANTS
> + /*
> + * All pages must be busied, not mapped, not valid (save the last one),
> + * not dirty and belong to the proper object.
> + */
> + for (int i = 0 ; i < count; i++) {
> + vm_page_assert_xbusied(m[i]);
> + KASSERT(!pmap_page_is_mapped(m[i]),
> + ("%s: page %p is mapped", __func__, m[i]));
> + KASSERT(m[i]->valid == 0 || i == count - 1,
> + ("%s: request for a valid page %p", __func__, m[i]));
Are you sure that e.g. the requested page cannot be partially valid ?
I am surprised.
> + KASSERT(m[i]->dirty == 0,
> + ("%s: page %p is dirty", __func__, m[i]));
> + KASSERT(m[i]->object == object,
> + ("%s: wrong object %p/%p", __func__, object, m[i]->object));
> + }
> +#endif
Create a helper function with the loop, and use it, instead of copying
the block twice.
> +
> + r = (*pagertab[object->type]->pgo_getpages)(object, m, count, reqpage);
> + if (r != VM_PAGER_OK)
> + return (r);
> +
> + /*
> + * If pager has replaced the page, assert that it had
> + * updated the array.
> + */
> + KASSERT(m[reqpage] == vm_page_lookup(object, m[reqpage]->pindex),
> + ("%s: mismatch page %p pindex %ju", __func__,
> + m[reqpage], (uintmax_t )m[reqpage]->pindex - 1));
Why -1 ?
Need an empty line after assert, to deliniate the code which is commented
about.
Also, you may assert that the requested page is still busied.
> + /*
> + * Pager didn't fill up entire page. Zero out
> + * partially filled data.
> + */
> + if (m[reqpage]->valid != VM_PAGE_BITS_ALL)
> + vm_page_zero_invalid(m[reqpage], TRUE);
> +
> + return (VM_PAGER_OK);
> +}
> +
> +int
> +vm_pager_get_pages_async(vm_object_t object, vm_page_t *m, int count,
> + int reqpage, pgo_getpages_iodone_t iodone, void *arg)
> +{
> +
> + VM_OBJECT_ASSERT_WLOCKED(object);
> + KASSERT(count > 0, ("%s: 0 count", __func__));
> +
> +#ifdef INVARIANTS
> + /*
> + * All pages must be busied, not mapped, not valid (save the last one),
> + * not dirty and belong to the proper object.
> + */
> + for (int i = 0 ; i < count; i++) {
> + vm_page_assert_xbusied(m[i]);
> + KASSERT(!pmap_page_is_mapped(m[i]),
> + ("%s: page %p is mapped", __func__, m[i]));
> + KASSERT(m[i]->valid == 0 || i == count - 1,
> + ("%s: request for a valid page %p", __func__, m[i]));
> + KASSERT(m[i]->dirty == 0,
> + ("%s: page %p is dirty", __func__, m[i]));
> + KASSERT(m[i]->object == object,
> + ("%s: wrong object %p/%p", __func__, object, m[i]->object));
> + }
> +#endif
> +
> + return ((*pagertab[object->type]->pgo_getpages_async)(object, m,
> + count, reqpage, iodone, arg));
> +}
> +
> +/*
> * vm_pager_put_pages() - inline, see vm/vm_pager.h
> * vm_pager_has_page() - inline, see vm/vm_pager.h
> */
> Index: sys/vm/vm_pager.h
> ===================================================================
> --- sys/vm/vm_pager.h (revision 284504)
> +++ sys/vm/vm_pager.h (working copy)
> @@ -106,9 +106,9 @@ vm_object_t vm_pager_allocate(objtype_t, void *, v
> vm_ooffset_t, struct ucred *);
> void vm_pager_bufferinit(void);
> void vm_pager_deallocate(vm_object_t);
> -static __inline int vm_pager_get_pages(vm_object_t, vm_page_t *, int, int);
> -static inline int vm_pager_get_pages_async(vm_object_t, vm_page_t *, int,
> - int, pgo_getpages_iodone_t, void *);
> +int vm_pager_get_pages(vm_object_t, vm_page_t *, int, int);
> +int vm_pager_get_pages_async(vm_object_t, vm_page_t *, int, int,
> + pgo_getpages_iodone_t, void *);
> static __inline boolean_t vm_pager_has_page(vm_object_t, vm_pindex_t, int *, int *);
> void vm_pager_init(void);
> vm_object_t vm_pager_object_lookup(struct pagerlst *, void *);
> @@ -115,40 +115,6 @@ vm_object_t vm_pager_object_lookup(struct pagerlst
> void vm_pager_free_nonreq(vm_object_t object, vm_page_t ma[], int reqpage,
> int npages, boolean_t object_locked);
>
> -/*
> - * vm_page_get_pages:
> - *
> - * Retrieve pages from the VM system in order to map them into an object
> - * ( or into VM space somewhere ). If the pagein was successful, we
> - * must fully validate it.
> - */
> -static __inline int
> -vm_pager_get_pages(
> - vm_object_t object,
> - vm_page_t *m,
> - int count,
> - int reqpage
> -) {
> - int r;
> -
> - VM_OBJECT_ASSERT_WLOCKED(object);
> - r = (*pagertab[object->type]->pgo_getpages)(object, m, count, reqpage);
> - if (r == VM_PAGER_OK && m[reqpage]->valid != VM_PAGE_BITS_ALL) {
> - vm_page_zero_invalid(m[reqpage], TRUE);
> - }
> - return (r);
> -}
> -
> -static inline int
> -vm_pager_get_pages_async(vm_object_t object, vm_page_t *m, int count,
> - int reqpage, pgo_getpages_iodone_t iodone, void *arg)
> -{
> -
> - VM_OBJECT_ASSERT_WLOCKED(object);
> - return ((*pagertab[object->type]->pgo_getpages_async)(object, m,
> - count, reqpage, iodone, arg));
> -}
> -
> static __inline void
> vm_pager_put_pages(
> vm_object_t object,
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