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Hi David Hildenbrand:<= /div>

>> From your description only I cannot tell how that would reall= y work.
>> Your description = of 1) indicated that we are dealing with an array to
>> manage memory segments, and arrays are a bad da= ta structure when it
>> come= s to sparsity.

In the baseline, it al= so manage memory by array(zone->free_area) in linux, as follows:
struct zone {
......
    struct free_area free_area[MA= X_ORDER];
}

"Multi_free_area"= would devide physical memory into serveral parts in zone by page-PFN,
and it also uses free_area to manage each parts of memory:
=
struct zone {
......
    struct free_area free_area[= flc][MAX_ORDER];  // flc def to 4
}

All the logic of memor= y-opt is unchange experts for that: select the corresponding freearea
to alloc-pages by allocation= -order which is to concentrate most of low-order-pages(almost
<= div>signal-page) all= ocation in the front area of physical memory and few memory-pollution in th= e
back area of the memory. Theoretically,  there will not be too much risk i think. 

Because i am not a expert so that maybe there are some case i have not considered and m= aybe
there are something wrong displeaed you in m= y email, pls don't take it ill.

=

>> J= ust always keep in mind that upstream Linux has a very broad community.
>> What might be "good eno= ugh" for smartphones might not be well suited for
>> servers, VMs, embedded devices, other archs .= .. just imagine the RAM
>> s= ize differences, sparse layout, dynamic memory changes, ...
 
&= gt;> Adding additional complexity to the buddy has to have a compelling<= /font>
>> benefit; keep in mind tha= t any complexity we introduce has to be
>> maintained in the long term.
 
>> Having t= hat said, starting with small steps is IMHO the right approach.

I will make the patch-series and try to make the= patch smaller and readable and
thanks your advices indeed.
=


=0A=

=0A=
lipeifeng@oppo.com
=0A=
 
Fr= om: David Hildenbrand
Date: 2021-04-28 17:04
C= C: linux-s390; <= a href=3D"mailto:linux-kernel@vger.kernel.org">linux-kernel; linux-mm
Subject: Re:= [RFC] mm: support multi_freearea to the reduction of external fragmentatio= n
>  >> Essentially CONFIG_SPARSEM= EM, whereby we can have huge holes in physical
=0A=
>  >> memory layout and memory areas coming/going with m= emory hot(un)plug.
=0A=
>  >> Usually we manage all metadata per section. For ex= ample, pageblocks are
=0A=
>  >> allocated per section. We avoid arrays that depend= on the
=0A=
>  >> initial/maximum physical memory size.
=0A=
>
=0A=
> CONFIG_SPRSEMEM has been opened in some of our product with =0A=
> Qcom-platform and
=0A=
> MTK platform. AFAIK, multi_freearea would not bring problem to =0A=
> it=EF=BC=9Fbecause the patch
=0A=
> just manage the physical memory of zone to serveral section(free_= area)
=0A=
> and adjust the
=0A=
> the range of pages-PFN for buddy-alloc-pages by the alloction-ord= er.
=0A=
> With memory
=0A=
> hot(un)plug, we would initialize the members of "multi_freea= rea" in zone.
=0A=
 
=0A=
From your description only I cannot tell how that would really work. =
=0A=
Your description of 1) indicated that we are dealing with an array to =
=0A=
manage memory segments, and arrays are a bad data structure when it =0A=
comes to sparsity.
=0A=
 
=0A=
>
=0A=
> The patch has been merged in the baseline of our product that has= been
=0A=
> sold all over the
=0A=
> world with Linux-4.4/4.9/4.19 so that i don't think there will be= too
=0A=
> much risk. Of course,
=0A=
> i might be wrong.
=0A=
 
=0A=
Just always keep in mind that upstream Linux has a very broad communit= y.
=0A=
What might be "good enough" for smartphones might not be wel= l suited for
=0A=
servers, VMs, embedded devices, other archs ... just imagine the RAM <= /div>=0A=
size differences, sparse layout, dynamic memory changes, ...
=0A=
 
=0A=
Adding additional complexity to the buddy has to have a compelling =0A=
benefit; keep in mind that any complexity we introduce has to be =0A=
maintained in the long term.
=0A=
 
=0A=
Having that said, starting with small steps is IMHO the right approach= .
=0A=
 
=0A=
--
=0A=
Thanks,
=0A=
 
=0A=
David / dhildenb
=0A=
 
=0A=
=0A= = ------=_001_NextPart254442525803_=------