| Message ID | 20230623164015.3431990-2-jiaqiyan@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Improve hugetlbfs read on HWPOISON hugepages | expand |
On Fri, Jun 23, 2023 at 04:40:12PM +0000, Jiaqi Yan wrote: > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries > are deleted from the llist. > > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s > from __update_and_free_hugetlb_folio and memory_failure won't need > explicit locking when freeing the raw_hwp_list. > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> (Sorry if stupid question...) folio_set_hugetlb_hwpoison() also calls llist_for_each_safe() but it still traverses the list without calling llist_del_all(). This convention applies only when removing item(s)? Thanks, Naoya Horiguchi > --- > mm/memory-failure.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 004a02f44271..c415c3c462a3 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio) > > static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > { > - struct llist_head *head; > - struct llist_node *t, *tnode; > + struct llist_node *t, *tnode, *head; > unsigned long count = 0; > > - head = raw_hwp_list_head(folio); > - llist_for_each_safe(tnode, t, head->first) { > + head = llist_del_all(raw_hwp_list_head(folio)); > + llist_for_each_safe(tnode, t, head) { > struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node); > > if (move_flag) > @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > kfree(p); > count++; > } > - llist_del_all(head); > return count; > } > > -- > 2.41.0.162.gfafddb0af9-goog > > >
On Fri, Jun 30, 2023 at 7:52 AM Naoya Horiguchi <naoya.horiguchi@linux.dev> wrote: > > On Fri, Jun 23, 2023 at 04:40:12PM +0000, Jiaqi Yan wrote: > > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries > > are deleted from the llist. > > > > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s > > from __update_and_free_hugetlb_folio and memory_failure won't need > > explicit locking when freeing the raw_hwp_list. > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > (Sorry if stupid question...) folio_set_hugetlb_hwpoison() also calls > llist_for_each_safe() but it still traverses the list without calling > llist_del_all(). This convention applies only when removing item(s)? I think in our previous discussion, Mike and I agree as of today's code in hugetlb.c and memory-failure.c, concurrent adding, deleting, traversing are fine with each other and with themselves [1], but new code need to be careful wrt ops on raw_hwp_list. This patch is a low-hanging fruit to ensure any caller of __folio_free_raw_hwp won't introduce any problem by correcting one thing in __folio_free_raw_hwp: since it wants to delete raw_hwp_page entries in the list, it should do it by first llist_del_all, and then kfree with a llist_for_each_safe. As for folio_set_hugetlb_hwpoison, I am not very comfortable fixing it. I imagine a way to fix it is llist_del_all() => llist_for_each_safe{...} => llist_add_batch(), or llist_add() within llist_for_each_safe{...}. I haven't really thought through if this is a correct fix. [1] https://lore.kernel.org/lkml/CACw3F51o1ZFSYZa+XLnk4Wwjy2w_q=Kn+aOQs0=qpfG-ZYDFKg@mail.gmail.com/#t > > Thanks, > Naoya Horiguchi > > > --- > > mm/memory-failure.c | 8 +++----- > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index 004a02f44271..c415c3c462a3 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio) > > > > static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > { > > - struct llist_head *head; > > - struct llist_node *t, *tnode; > > + struct llist_node *t, *tnode, *head; > > unsigned long count = 0; > > > > - head = raw_hwp_list_head(folio); > > - llist_for_each_safe(tnode, t, head->first) { > > + head = llist_del_all(raw_hwp_list_head(folio)); > > + llist_for_each_safe(tnode, t, head) { > > struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node); > > > > if (move_flag) > > @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > kfree(p); > > count++; > > } > > - llist_del_all(head); > > return count; > > } > > > > -- > > 2.41.0.162.gfafddb0af9-goog > > > > > >
On Fri, Jun 30, 2023 at 01:59:23PM -0700, Jiaqi Yan wrote: > On Fri, Jun 30, 2023 at 7:52 AM Naoya Horiguchi > <naoya.horiguchi@linux.dev> wrote: > > > > On Fri, Jun 23, 2023 at 04:40:12PM +0000, Jiaqi Yan wrote: > > > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries > > > are deleted from the llist. > > > > > > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s > > > from __update_and_free_hugetlb_folio and memory_failure won't need > > > explicit locking when freeing the raw_hwp_list. > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > > > (Sorry if stupid question...) folio_set_hugetlb_hwpoison() also calls > > llist_for_each_safe() but it still traverses the list without calling > > llist_del_all(). This convention applies only when removing item(s)? > > I think in our previous discussion, Mike and I agree as of today's > code in hugetlb.c and memory-failure.c, concurrent adding, deleting, > traversing are fine with each other and with themselves [1], but new > code need to be careful wrt ops on raw_hwp_list. > > This patch is a low-hanging fruit to ensure any caller of > __folio_free_raw_hwp won't introduce any problem by correcting one > thing in __folio_free_raw_hwp: since it wants to delete raw_hwp_page > entries in the list, it should do it by first llist_del_all, and then > kfree with a llist_for_each_safe. Thanks for the explanation, this is worth adding to the patch description for future developers to understand the background. > > As for folio_set_hugetlb_hwpoison, I am not very comfortable fixing > it. I imagine a way to fix it is llist_del_all() => > llist_for_each_safe{...} => llist_add_batch(), or llist_add() within > llist_for_each_safe{...}. I haven't really thought through if this is > a correct fix. I see. Changing folio_set_hugetlb_hwpoison() like this is a little too complex considering that this fix is for precaution. So no change on this for now is fine to me. Anyway this patch looks fine to me. Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > > [1] https://lore.kernel.org/lkml/CACw3F51o1ZFSYZa+XLnk4Wwjy2w_q=Kn+aOQs0=qpfG-ZYDFKg@mail.gmail.com/#t > > > > > > Thanks, > > Naoya Horiguchi > > > > > --- > > > mm/memory-failure.c | 8 +++----- > > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > > index 004a02f44271..c415c3c462a3 100644 > > > --- a/mm/memory-failure.c > > > +++ b/mm/memory-failure.c > > > @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio) > > > > > > static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > > { > > > - struct llist_head *head; > > > - struct llist_node *t, *tnode; > > > + struct llist_node *t, *tnode, *head; > > > unsigned long count = 0; > > > > > > - head = raw_hwp_list_head(folio); > > > - llist_for_each_safe(tnode, t, head->first) { > > > + head = llist_del_all(raw_hwp_list_head(folio)); > > > + llist_for_each_safe(tnode, t, head) { > > > struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node); > > > > > > if (move_flag) > > > @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > > kfree(p); > > > count++; > > > } > > > - llist_del_all(head); > > > return count; > > > } > > > > > > -- > > > 2.41.0.162.gfafddb0af9-goog > > > > > > > > >
On 06/23/23 16:40, Jiaqi Yan wrote: > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries > are deleted from the llist. > > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s > from __update_and_free_hugetlb_folio and memory_failure won't need > explicit locking when freeing the raw_hwp_list. > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > --- > mm/memory-failure.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) After updating the reason for patch in commit message as suggested by Naoya, Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
On Wed, Jul 5, 2023 at 4:36 PM Mike Kravetz <mike.kravetz@oracle.com> wrote: > > On 06/23/23 16:40, Jiaqi Yan wrote: > > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries > > are deleted from the llist. > > > > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s > > from __update_and_free_hugetlb_folio and memory_failure won't need > > explicit locking when freeing the raw_hwp_list. > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > --- > > mm/memory-failure.c | 8 +++----- > > 1 file changed, 3 insertions(+), 5 deletions(-) > > After updating the reason for patch in commit message as suggested by Naoya, Thank you both Mike and Naoya! I will add the explanation in the next version. > > Acked-by: Mike Kravetz <mike.kravetz@oracle.com> > > -- > Mike Kravetz > > > > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index 004a02f44271..c415c3c462a3 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio) > > > > static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > { > > - struct llist_head *head; > > - struct llist_node *t, *tnode; > > + struct llist_node *t, *tnode, *head; > > unsigned long count = 0; > > > > - head = raw_hwp_list_head(folio); > > - llist_for_each_safe(tnode, t, head->first) { > > + head = llist_del_all(raw_hwp_list_head(folio)); > > + llist_for_each_safe(tnode, t, head) { > > struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node); > > > > if (move_flag) > > @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) > > kfree(p); > > count++; > > } > > - llist_del_all(head); > > return count; > > } > > > > -- > > 2.41.0.162.gfafddb0af9-goog > >
diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 004a02f44271..c415c3c462a3 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio) static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) { - struct llist_head *head; - struct llist_node *t, *tnode; + struct llist_node *t, *tnode, *head; unsigned long count = 0; - head = raw_hwp_list_head(folio); - llist_for_each_safe(tnode, t, head->first) { + head = llist_del_all(raw_hwp_list_head(folio)); + llist_for_each_safe(tnode, t, head) { struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node); if (move_flag) @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) kfree(p); count++; } - llist_del_all(head); return count; }
Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries are deleted from the llist. llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s from __update_and_free_hugetlb_folio and memory_failure won't need explicit locking when freeing the raw_hwp_list. Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> --- mm/memory-failure.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)