Messages in this thread | | | Date | Mon, 27 Dec 2021 14:14:53 +0800 | Subject | Re: [PATCH 1/3] mm: vmalloc: Let user to control huge vmalloc default behavior | From | Kefeng Wang <> |
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On 2021/12/27 11:19, Matthew Wilcox wrote: > On Mon, Dec 27, 2021 at 09:44:24AM +0800, Kefeng Wang wrote: >> On 2021/12/27 1:36, Christophe Leroy wrote: >>> Le 26/12/2021 à 09:39, Kefeng Wang a écrit : >>>> Add HUGE_VMALLOC_DEFAULT_ENABLED to let user to choose whether or >>>> not enable huge vmalloc mappings by default, and this could make >>>> more architectures to enable huge vmalloc mappings feature but >>>> don't want to enable it by default. >>>> >>>> Add hugevmalloc=on/off parameter to enable or disable this feature >>>> at boot time, nohugevmalloc is still supported and equivalent to >>>> hugevmalloc=off. >>> Is there a real added value to have the user be able to select that ? >>> >>> If the architecture supports it, is there any good reason to not use it ? >> There are some disadvantages[1], one of the main concerns is the possible >> >> memory waste, we have backported this feature to our kernel 5.10, but our >> >> downstream in our some scenario(especially in embedded), they don't want >> >> it enabled by default, and others want it, this is why patch1 comes. >> >>> Why not just do like PPC and enable it by default ? Why should it be >>> enabled by default on PPC but disabled by default on ARM64 and X86 ? >> The PPC is default enabled, we don't changes this behavior. >> >> Maybe upstream is not care about this, as I said in cover-letter, if >> arm64/x86 >> >> don't want patch1, we could only just select config to enable it. >> >> Let's wait for more feedback. > We should not have different defaults by architecture. Either we change > the default for PPC, or x86 & arm should have the same default as PPC.
Ok, since HUGE_VMALLOC_DEFAULT_ENABLED is introduced, we could make it
default y, not only select it on PPC, then the ppc/arm64/x86 have same default value.
And if someone don't want it, they could not enable this config.
Meanwhile hugevmalloc=on/off to make this feature to enable/disable at boot time.
I will add some explanation and resend it, thanks.
> .
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