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Wed, 27 Jan 2021 12:21:47 -0800 (PST) Sender: Minchan Kim Date: Wed, 27 Jan 2021 12:21:45 -0800 From: Minchan Kim To: Michal Hocko Cc: Andrew Morton , linux-mm , LKML , hyesoo.yu@samsung.com, david@redhat.com, surenb@google.com, pullip.cho@samsung.com, joaodias@google.com, hridya@google.com, john.stultz@linaro.org, sumit.semwal@linaro.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, hch@infradead.org, robh+dt@kernel.org, linaro-mm-sig@lists.linaro.org Subject: Re: [PATCH v4 1/4] mm: cma: introduce gfp flag in cma_alloc instead of no_warn Message-ID: References: <20210121175502.274391-1-minchan@kernel.org> <20210121175502.274391-2-minchan@kernel.org> <20210125130701.GF827@dhcp22.suse.cz> <20210126073808.GZ827@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Tue, Jan 26, 2021 at 11:12:14AM -0800, Minchan Kim wrote: > On Tue, Jan 26, 2021 at 08:38:08AM +0100, Michal Hocko wrote: > > On Mon 25-01-21 11:42:34, Minchan Kim wrote: > > > On Mon, Jan 25, 2021 at 02:07:01PM +0100, Michal Hocko wrote: > > > > On Thu 21-01-21 09:54:59, Minchan Kim wrote: > > > > > The upcoming patch will introduce __GFP_NORETRY semantic > > > > > in alloc_contig_range which is a failfast mode of the API. > > > > > Instead of adding a additional parameter for gfp, replace > > > > > no_warn with gfp flag. > > > > > > > > > > To keep old behaviors, it follows the rule below. > > > > > > > > > > no_warn gfp_flags > > > > > > > > > > false GFP_KERNEL > > > > > true GFP_KERNEL|__GFP_NOWARN > > > > > gfp & __GFP_NOWARN GFP_KERNEL | (gfp & __GFP_NOWARN) > > > > > > > > > > Reviewed-by: Suren Baghdasaryan > > > > > Signed-off-by: Minchan Kim > > > > [...] > > > > > diff --git a/mm/cma.c b/mm/cma.c > > > > > index 0ba69cd16aeb..d50627686fec 100644 > > > > > --- a/mm/cma.c > > > > > +++ b/mm/cma.c > > > > > @@ -419,13 +419,13 @@ static inline void cma_debug_show_areas(struct cma *cma) { } > > > > > * @cma: Contiguous memory region for which the allocation is performed. > > > > > * @count: Requested number of pages. > > > > > * @align: Requested alignment of pages (in PAGE_SIZE order). > > > > > - * @no_warn: Avoid printing message about failed allocation > > > > > + * @gfp_mask: GFP mask to use during the cma allocation. > > > > > > > > Call out supported gfp flags explicitly. Have a look at kvmalloc_node > > > > for a guidance. > > > > > > How about this? > > > > > > > > > diff --git a/mm/cma.c b/mm/cma.c > > > index d50627686fec..b94727b694d6 100644 > > > --- a/mm/cma.c > > > +++ b/mm/cma.c > > > @@ -423,6 +423,10 @@ static inline void cma_debug_show_areas(struct cma *cma) { } > > > * > > > * This function allocates part of contiguous memory on specific > > > * contiguous memory area. > > > + * > > > + * For gfp_mask, GFP_KERNEL and __GFP_NORETRY are supported. __GFP_NORETRY > > > + * will avoid costly functions(e.g., waiting on page_writeback and locking) > > > + * at current implementaion during the page migration. > > > > rather than explicitly mentioning what the flag implies I think it would > > be more useful to state the intended usecase. See how kvmalloc_node says > > "__GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is > > preferable to the vmalloc fallback, due to visible performance > > drawbacks. > > __GFP_NOWARN is also supported to suppress allocation failure messages." > > > > This would help people not familiar with internals to see whether this > > flag is a good fit for them. > > > > In this case I woul go with > > " > > @flags: gfp mask. Must be compatible (superset) with GFP_KERNEL. > > [...] > > Reclaim modifiers (__GFP_RETRY_MAYFAIL, __GFP_NOFAIL) are not supported. > > __GFP_NORETRY is supported, and it should be used for opportunistic > > allocation attempts that should rather fail quickly when the caller has > > a fallback strategy. > > " > > > > Obviously for this patch you will go with a simple statement that > > Reclaim modifiers are not supported at all. > > After more discussion for gfp_flags in thread of next patch, let me > changes a bit more based on it. > > Thanks for the suggestion, Michal. Based on the discussion in other thread, I want to go with __GFP_NORETRY to indicate "opportunistic-easy-to-fail attempt" so suggestion words Michal is valid so I will carry it on next version. Thank you.