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Date: Wed, 4 Jul 2018 12:35:02 +0530
From: ritesh sonawane <rdssonawane2317@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Changing MMAP_THRESHOLD in malloc() implementation.

sir above statistics are with 64MB page size. we are using system which
having 2MB(large page)
64MB(huge page).

On Wed, Jul 4, 2018 at 10:54 AM, ritesh sonawane <rdssonawane2317@...il.com>
wrote:

> Thank you very much for instant reply..
>
> Yes sir it is wasting memory for each shared library. But memory wastage
> even worse when program
> requesting memory with size more than 224KB(threshold value).
>
> ->If a program requests 1GB per request, it can use 45GB at the most.
> ->If a program requests 512MB per request, it can use 41.5GB at the most.
> ->If a program requests 225KB per request, it can use about 167MB at the
> most.
>
> As we ported  musl-1.1.14 for our architecture, we are bounded to make
> change in same base code.
> we have increased  MMAP_THRESHOLD to 1GB and also changes the calculation
> for bin index .
> after that observed improvement in memory utilization. i.e for size 225KB
> memory used is 47.6 GB.
>
> But now facing problem in multi threaded application. As we haven't
> changed the function pretrim()
> because there are some hard coded values like '40' and '3' used and
> unable to understand how
> these values are decided ..?
>
> static int pretrim(struct chunk *self, size_t n, int i, int j)
> {
>         size_t n1;
>         struct chunk *next, *split;
>
>         /* We cannot pretrim if it would require re-binning. */
>         if (j < 40) return 0;
>         if (j < i+3) {
>                 if (j != 63) return 0;
>                 n1 = CHUNK_SIZE(self);
>                 if (n1-n <= MMAP_THRESHOLD) return 0;
>         } else {
>                 n1 = CHUNK_SIZE(self);
>         }
>  .....
>  .....
> ......
> }
>
> can we get any clue how these value are decided, it will be very
> helpful for us.
>
> Best Regard,
> Ritesh Sonawane
>
> On Tue, Jul 3, 2018 at 8:13 PM, Rich Felker <dalias@...c.org> wrote:
>
>> On Tue, Jul 03, 2018 at 12:58:04PM +0530, ritesh sonawane wrote:
>> > Hi All,
>> >
>> > We are using musl-1.1.14 version for our architecture. It is having page
>> > size of 2MB.
>> > Due to low threshold value there is more memory wastage. So we want to
>> > change the value of  MMAP_THRESHOLD.
>> >
>> > can anyone please giude us, which factor need to consider to change this
>> > threshold value ?
>>
>> It's not a parameter that can be changed but linked to the scale of
>> bin sizes. There is no framework to track and reuse freed chunks which
>> are larger than MMAP_THRESHOLD, so you'd be replacing recoverable
>> waste from page granularity with unrecoverable waste from inability to
>> reuse these larger freed chunks except breaking them up into pieces to
>> satisfy smaller requests.
>>
>> I may look into handling this better when replacing musl's malloc at
>> some point, but if your system forces you to use ridiculously large
>> pages like 2MB, you've basically committed to wasting huge amounts of
>> memory anyway (at least 2MB for each shared library in each
>> process)...
>>
>> With musl git-master and future releases, you have the option to link
>> a malloc replacement library that might be a decent solution to your
>> problem.
>>
>> Rich
>>
>
>

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