| Message ID | 20231031140741.79387-10-chengming.zhou@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | slub: Delay freezing of CPU partial slabs | expand |
On 10/31/23 15:07, chengming.zhou@linux.dev wrote: > From: Chengming Zhou <zhouchengming@bytedance.com> > > The current updated scheme (which this series implemented) is: > - node partial slabs: PG_Workingset && !frozen > - cpu partial slabs: !PG_Workingset && !frozen > - cpu slabs: !PG_Workingset && frozen > - full slabs: !PG_Workingset && !frozen It could be useful to put this also to the initial comment description. Towards the end of the comment, there's a block explaining "slab->frozen". It could be extended to cover all 4 combination (but not all of them need such long explanation). > > The most important change is that "frozen" bit is not set for the > cpu partial slabs anymore, __slab_free() will grab node list_lock > then check by !PG_Workingset that it's not on a node partial list. > > And the "frozen" bit is still kept for the cpu slabs for performance, > since we don't need to grab node list_lock to check whether the > PG_Workingset is set or not if the "frozen" bit is set in __slab_free(). > > Update related documentations and comments in the source. > > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > --- > mm/slub.c | 16 ++++++++++++---- > 1 file changed, 12 insertions(+), 4 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index bb7368047103..89d3f7a18a73 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -76,13 +76,22 @@ > * > * Frozen slabs > * > - * If a slab is frozen then it is exempt from list management. It is not > - * on any list except per cpu partial list. The processor that froze the > + * If a slab is frozen then it is exempt from list management. It is > + * the cpu slab which is actively allocated from by the processor that > + * froze it and it is not on any list. The processor that froze the > * slab is the one who can perform list operations on the slab. Other > * processors may put objects onto the freelist but the processor that > * froze the slab is the only one that can retrieve the objects from the > * slab's freelist. > * > + * CPU partial slabs > + * > + * The partially empty slabs cached on the CPU partial list are used > + * for performance reasons, which speeds up the allocation process. > + * These slabs are not frozen, but also exempt from list management, ^ are also (otherwise somebody could read it as "also are not") > + * by clearing the PG_workingset flag when moving out of the node > + * partial list. Please see __slab_free() for more details. > + * > * list_lock > * > * The list_lock protects the partial and full list on each node and > @@ -2620,8 +2629,7 @@ static void put_partials_cpu(struct kmem_cache *s, > } > > /* > - * Put a slab that was just frozen (in __slab_free|get_partial_node) into a > - * partial slab slot if available. > + * Put a slab into a partial slab slot if available. > * > * If we did not find a slot then simply move all the partials to the > * per node partial list.
On 2023/11/1 21:51, Vlastimil Babka wrote: > On 10/31/23 15:07, chengming.zhou@linux.dev wrote: >> From: Chengming Zhou <zhouchengming@bytedance.com> >> >> The current updated scheme (which this series implemented) is: >> - node partial slabs: PG_Workingset && !frozen >> - cpu partial slabs: !PG_Workingset && !frozen >> - cpu slabs: !PG_Workingset && frozen >> - full slabs: !PG_Workingset && !frozen > > It could be useful to put this also to the initial comment description. > Towards the end of the comment, there's a block explaining > "slab->frozen". It could be extended to cover all 4 combination (but not > all of them need such long explanation). > Ok, I will extend it and put in the cover letter of v5. >> >> The most important change is that "frozen" bit is not set for the >> cpu partial slabs anymore, __slab_free() will grab node list_lock >> then check by !PG_Workingset that it's not on a node partial list. >> >> And the "frozen" bit is still kept for the cpu slabs for performance, >> since we don't need to grab node list_lock to check whether the >> PG_Workingset is set or not if the "frozen" bit is set in __slab_free(). >> >> Update related documentations and comments in the source. >> >> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> >> --- >> mm/slub.c | 16 ++++++++++++---- >> 1 file changed, 12 insertions(+), 4 deletions(-) >> >> diff --git a/mm/slub.c b/mm/slub.c >> index bb7368047103..89d3f7a18a73 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -76,13 +76,22 @@ >> * >> * Frozen slabs >> * >> - * If a slab is frozen then it is exempt from list management. It is not >> - * on any list except per cpu partial list. The processor that froze the >> + * If a slab is frozen then it is exempt from list management. It is >> + * the cpu slab which is actively allocated from by the processor that >> + * froze it and it is not on any list. The processor that froze the >> * slab is the one who can perform list operations on the slab. Other >> * processors may put objects onto the freelist but the processor that >> * froze the slab is the only one that can retrieve the objects from the >> * slab's freelist. >> * >> + * CPU partial slabs >> + * >> + * The partially empty slabs cached on the CPU partial list are used >> + * for performance reasons, which speeds up the allocation process. >> + * These slabs are not frozen, but also exempt from list management, > > ^ are also > > (otherwise somebody could read it as "also are not") > Ah, will fix. Thanks!
diff --git a/mm/slub.c b/mm/slub.c index bb7368047103..89d3f7a18a73 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -76,13 +76,22 @@ * * Frozen slabs * - * If a slab is frozen then it is exempt from list management. It is not - * on any list except per cpu partial list. The processor that froze the + * If a slab is frozen then it is exempt from list management. It is + * the cpu slab which is actively allocated from by the processor that + * froze it and it is not on any list. The processor that froze the * slab is the one who can perform list operations on the slab. Other * processors may put objects onto the freelist but the processor that * froze the slab is the only one that can retrieve the objects from the * slab's freelist. * + * CPU partial slabs + * + * The partially empty slabs cached on the CPU partial list are used + * for performance reasons, which speeds up the allocation process. + * These slabs are not frozen, but also exempt from list management, + * by clearing the PG_workingset flag when moving out of the node + * partial list. Please see __slab_free() for more details. + * * list_lock * * The list_lock protects the partial and full list on each node and @@ -2620,8 +2629,7 @@ static void put_partials_cpu(struct kmem_cache *s, } /* - * Put a slab that was just frozen (in __slab_free|get_partial_node) into a - * partial slab slot if available. + * Put a slab into a partial slab slot if available. * * If we did not find a slot then simply move all the partials to the * per node partial list.