linux-kernel - Re: [PATCH v2] lib: Replace kmap() with kmap_local

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Date:   Tue, 13 Jun 2023 14:08:47 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Sumitra Sharma <sumitraartsy@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
CC:     Ira Weiny <ira.weiny@...el.com>, Fabio <fmdefrancesco@...il.com>,
        "Deepak R Varma" <drv@...lo.com>
Subject: Re: [PATCH v2] lib: Replace kmap() with kmap_local_page()

Sumitra Sharma wrote:
> kmap() has been deprecated in favor of the kmap_local_page()
> due to high cost, restricted mapping space, the overhead of
> a global lock for synchronization, and making the process
> sleep in the absence of free slots.
> 
> kmap_local_page() is faster than kmap() and offers thread-local
> and CPU-local mappings, take pagefaults in a local kmap region
> and preserves preemption by saving the mappings of outgoing
> tasks and restoring those of the incoming one during a context
> switch.
> 
> The mappings are kept thread local in the functions
> “dmirror_do_read” and “dmirror_do_write” in test_hmm.c
> 
> Therefore, replace kmap() with kmap_local_page() and use
> mempcy_from/to_page() to avoid open coding kmap_local_page()
> + memcpy() + kunmap_local().
> 
> Remove the unused variable “tmp”.
> 
> 
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> 
> Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>

LGTM

Reviewed-by: Ira Weiny <ira.weiny@...el.com>