Messages in this thread | | | From | SeongJae Park <> | Subject | Re: [RFC PATCH v1 2/3] mm/damon/core: Add damon_start_one() | Date | Tue, 22 Feb 2022 09:53:28 +0000 |
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Hello Jonghyeon,
On Fri, 18 Feb 2022 19:26:10 +0900 Jonghyeon Kim <tome01@ajou.ac.kr> wrote:
> damon_start() function is designed to start multiple damon monitoring > contexts. But, sometimes we need to start monitoring one context. > Although __damon_start() could be considered to start for one monitoring > context, it seems reasonable to adopt a new function that does not need > to handle 'damon_lock' from the caller. > > Signed-off-by: Jonghyeon Kim <tome01@ajou.ac.kr> > --- > include/linux/damon.h | 1 + > mm/damon/core.c | 25 +++++++++++++++++++++++++ > 2 files changed, 26 insertions(+) > > diff --git a/include/linux/damon.h b/include/linux/damon.h > index c0adf1566603..069577477662 100644 > --- a/include/linux/damon.h > +++ b/include/linux/damon.h > @@ -511,6 +511,7 @@ int damon_register_ops(struct damon_operations *ops); > int damon_select_ops(struct damon_ctx *ctx, enum damon_ops_id id); > > int damon_start(struct damon_ctx **ctxs, int nr_ctxs); > +int damon_start_one(struct damon_ctx *ctx); > int damon_stop(struct damon_ctx **ctxs, int nr_ctxs); > > #endif /* CONFIG_DAMON */ > diff --git a/mm/damon/core.c b/mm/damon/core.c > index 290c9c0535ee..e43f138a3489 100644 > --- a/mm/damon/core.c > +++ b/mm/damon/core.c > @@ -466,6 +466,31 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs) > return err; > } > > +/** > + * damon_start_one() - Starts the monitorings for one context. > + * @ctx: monitoring context > + * > + * This function starts one monitoring thread for only one monitoring context > + * handling damon_lock. > + * > + * Return: 0 on success, negative error code otherwise. > + */ > +int damon_start_one(struct damon_ctx *ctx) > +{ > + int err = 0; > + > + mutex_lock(&damon_lock); > + err = __damon_start(ctx); > + if (err) { > + mutex_unlock(&damon_lock); > + return err; > + } > + nr_running_ctxs++; > + mutex_unlock(&damon_lock); > + > + return err; > +} > +
IMHO, this looks like an unnecessary duplication of code. Unless this is needed for a real usecase, this change might unnecessarily make the code only a little bit more complicated. And to my understanding of the next patch, this is not really needed for this patchset. I will left comments on the patch. If I'm missing something, please clarify why this is really needed.
Furthermore, damon_start() starts a set of DAMON contexts in exclusive manner, to ensure there will be no interference. This patch breaks the assumption. That is, contexts that started with damon_start() could be interfered by other contexts that started with damon_start_one(). I have a plan to make damon_start() also work for non-exclusive contexts group[1], though.
[1] https://lore.kernel.org/linux-mm/20220217161938.8874-3-sj@kernel.org/
Thanks, SJ
> /* > * __damon_stop() - Stops monitoring of given context. > * @ctx: monitoring context > -- > 2.17.1 >
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