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From: Igor Munkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>
To: Sergey Kaplun <skaplun@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org
Subject: Re: [Tarantool-patches] [PATCH luajit 2/2] Linux/ARM64: Make mremap() non-moving due to VA space woes.
Date: Sun, 1 Aug 2021 13:36:33 +0300
Message-ID: <20210801103633.GX27855@tarantool.org> (raw)
In-Reply-To: <YQFNso1z3FAbd/5L@root>

Sergey,

Thanks for the fixes! LGTM, except the single typo.

On 28.07.21, Sergey Kaplun wrote:

<snipped>

> 
> The new commit message is the following:
> 
> ===================================================================
> Linux/ARM64: Make mremap() non-moving due to VA space woes.
> 
> This reduces overall performance on ARM64, but we have no choice.
> Linux kernel default userspace VA is 48 bit, but we'd need 47 bit.
> mremap() ignores address hints due to a kernel API issue. The mapping
> may move to an undesired address which will cause an assert or crash.
> 
> Reported by Raymond W. Ko.
> 
> (cherry picked from commit 67dbec82f4f05a416a78a560a726553beaa7a223)
> 
> 47-bit VA space is required by LuaJIT for keeping a GC object pointer in
> TValue. In case of huge blobs that are mapped directly, `mremap()` may
> move the chunk out of 47-bit range of VA space on ARM64. `mremap()`
> accepts the fifth argument (new address hint) only with MREMAP_FIXED
> flag. In that case it unmaps any other mapping to specified address.
> 
> To avoid this behaviour this patch restricts `mremap()` to relocate
> the mapping to a new virtual address by set CALL_MREMAP_NOMOVE flag

Typo: s/set/setting/.

> instead of CALL_MREMAP_MAYMOVE for arm64 architecture.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Needed for tarantool/tarantool#6154

Minor: Why #5629 is not mentioned?

> ===================================================================
> 

<snipped>

> 
> -- 
> Best regards,
> Sergey Kaplun

-- 
Best regards,
IM

  reply	other threads:[~2021-08-01 11:00 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-06 17:40 [Tarantool-patches] [PATCH luajit 0/2] arm64: fix 48-bit addresses issues Sergey Kaplun via Tarantool-patches
2021-07-06 17:40 ` [Tarantool-patches] [PATCH luajit 1/2] Add support for full-range 64 bit lightuserdata Sergey Kaplun via Tarantool-patches
2021-07-27 13:59   ` Igor Munkin via Tarantool-patches
2021-07-28 12:29     ` Sergey Kaplun via Tarantool-patches
2021-08-01 10:36       ` Igor Munkin via Tarantool-patches
2021-08-02 14:56         ` Sergey Kaplun via Tarantool-patches
2021-08-01 16:25       ` Sergey Ostanevich via Tarantool-patches
2021-08-02 14:51         ` Sergey Kaplun via Tarantool-patches
2021-08-02 15:42           ` Igor Munkin via Tarantool-patches
2021-08-10 16:46           ` Sergey Ostanevich via Tarantool-patches
2021-08-11  5:54             ` Vitaliia Ioffe via Tarantool-patches
2021-07-06 17:40 ` [Tarantool-patches] [PATCH luajit 2/2] Linux/ARM64: Make mremap() non-moving due to VA space woes Sergey Kaplun via Tarantool-patches
2021-07-27 15:23   ` Igor Munkin via Tarantool-patches
2021-07-28 12:29     ` Sergey Kaplun via Tarantool-patches
2021-08-01 10:36       ` Igor Munkin via Tarantool-patches [this message]
2021-08-01 16:59         ` Sergey Ostanevich via Tarantool-patches
2021-08-02 15:08           ` Sergey Kaplun via Tarantool-patches
2021-08-02 15:55             ` Sergey Ostanevich via Tarantool-patches
2021-08-02 15:11         ` Sergey Kaplun via Tarantool-patches
2021-08-11  7:21 ` [Tarantool-patches] [PATCH luajit 0/2] arm64: fix 48-bit addresses issues Igor Munkin via Tarantool-patches

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