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charset="utf-8" Content-Transfer-Encoding: quoted-printable body { line-height: 1.5; }blockquote { margin-top: 0px; margin-bottom:= 0px; margin-left: 0.5em; }body { font-size: 10.5pt; font-family: 'Microsof= t YaHei UI'; color: rgb(0, 0, 0); line-height: 1.5; }= =0A=
Hi Andrew Morton=EF=BC=9A

> Unfortunately this part of the code is undergoing a lot of cha= nge
> lately.  How serious is this problem?  Please = tell us how often the
> problem is being observed, under what = circumstances, etc.
=0A=

I have observed some problems in process-TIF_32BIT, such as Wechat
and others Android = ;APP.

In the above processes which the single largest&nb= sp;remaining free-addr-space
is 12Mbytes in some case, we found th= at the processes wound fail to al= loc
a 12Mbytes(align 1M) in= the old methods so that Out-of-Memory.

The idea of this patch is the same as the following patch whic= h is used for
unmapped_area_topdown, as fo= llows:

Thank y= ou very much indeed to ask such nice question and I wish I have given
a clear reply. Pls let me know If there are any pr= oblems you found.

=0A=
lipeifeng@oppo.com
=0A=
 
Fr= om: Andrew Morton=
Date: 2022-04-21 05:57
To:&nbs= p;lipeifeng
Su= bject: Re: [PATCH] mm: modify the method to search addr in unmappe= d_area
On Wed, 20 Apr 2022 16:40:39 +0800 lipeif= eng@oppo.com wrote:
=0A=
 
=0A=
> The old method will firstly find the space in len(info->length=
=0A=
> + info->align_mask), and get address at the desired alignment.=
=0A=
>
=0A=
> Sometime, addr  would be failed if there are enough
=0A=
> addr space in kernel by above method, e.g., you can't get a
= =0A=
> addr sized in 1Mbytes, align_mask 1Mbytes successfully although=0A=
> there are still (2M-1)bytes space in kernel.
=0A=
>
=0A=
> This patch would fix thr problem above by the new method: find th= e
=0A=
> space in info->length and judge if at the desired info->ali= gn_mask
=0A=
> at the same time.
=0A=
>
=0A=
> Do a simple test in TIF_32BIT with unmapped_area:
=0A=
> - Try to take addr (size:1M align:2M) until allocation fails;=0A=
> - Try to take addr (size:1M align:1M) and account how to space ca= n
=0A=
> be alloced successfully.
=0A=
>
=0A=
> Before optimization: alloced 0     bytes.=0A=
> After  optimization: alloced 1.9+G bytes.
=0A=
 
=0A=
Thanks.
=0A=
 
=0A=
Unfortunately this part of the code is undergoing a lot of change=0A=
lately.  How serious is this problem?  Please tell us how of= ten the
=0A=
problem is being observed, under what circumstances, etc.
=0A=
 
=0A=
=0A= = ------=_001_NextPart325128532342_=------