Hi Andrew Morton：
> Unfortunately this part of the code is undergoing a lot of change
> lately. How serious is this problem? Please tell us how often the
> problem is being observed, under what circumstances, etc.
I have observed some problems in process-TIF_32BIT, such as Wechat
and others Android APP.
In the above processes which the single largest remaining free-addr-space
is 12Mbytes in some case, we found that the processes wound fail to alloc
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 which is used for
unmapped_area_topdown, as follows:
Thank you 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 problems you found.
lipeifeng@xxxxxxxx
From: Andrew MortonDate: 2022-04-21 05:57To: lipeifengSubject: Re: [PATCH] mm: modify the method to search addr in unmapped_areaOn Wed, 20 Apr 2022 16:40:39 +0800 lipeifeng@xxxxxxxx wrote:> The old method will firstly find the space in len(info->length> + info->align_mask), and get address at the desired alignment.>> Sometime, addr would be failed if there are enough> addr space in kernel by above method, e.g., you can't get a> addr sized in 1Mbytes, align_mask 1Mbytes successfully although> there are still (2M-1)bytes space in kernel.>> This patch would fix thr problem above by the new method: find the> space in info->length and judge if at the desired info->align_mask> at the same time.>> Do a simple test in TIF_32BIT with unmapped_area:> - Try to take addr (size:1M align:2M) until allocation fails;> - Try to take addr (size:1M align:1M) and account how to space can> be alloced successfully.>> Before optimization: alloced 0 bytes.> After optimization: alloced 1.9+G bytes.Thanks.Unfortunately this part of the code is undergoing a lot of changelately. How serious is this problem? Please tell us how often theproblem is being observed, under what circumstances, etc.
