linux-kernel - Re: [RFC 2/6] PM: Hibernate: Add option to disable disk offset randomization

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Message-ID: <YoTt6C5ymvmMcmWw@infradead.org>
Date:   Wed, 18 May 2022 06:00:24 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Vivek Kumar <quic_vivekuma@...cinc.com>
Cc:     corbet@....net, catalin.marinas@....com, will@...nel.org,
        tglx@...utronix.de, maz@...nel.org, axboe@...nel.dk,
        rafael@...nel.org, akpm@...ux-foundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-mm@...ck.org, len.brown@...el.com,
        pavel@....cz, paulmck@...nel.org, bp@...e.de,
        keescook@...omium.org, songmuchun@...edance.com,
        rdunlap@...radead.org, damien.lemoal@...nsource.wdc.com,
        pasha.tatashin@...een.com, tabba@...gle.com, ardb@...nel.org,
        tsoni@...cinc.com, quic_psodagud@...cinc.com,
        quic_svaddagi@...cinc.com,
        Prasanna Kumar <quic_kprasan@...cinc.com>
Subject: Re: [RFC 2/6] PM: Hibernate: Add option to disable disk offset
 randomization

On Wed, May 18, 2022 at 01:18:37PM +0530, Vivek Kumar wrote:
> Add a kernel parameter to disable the disk offset randomization
> for SSD devices in which such feature is available at the
> firmware level. This is helpful in improving hibernation
> resume time.

This patch just adds a global variable which is then entirely
igored.

But the idea of "randomizing" offsets on SSDs sounds like complete BS to
start with.  The whole job of the SSD is to remap from a random writable
block device to difference physical blocks to deal with erases and wear
leveling.  In other words it really doesn't matter what offset your
write to.  That being said I could not actually find any code that does
this randomization to start with, but that might just be my lack of grep
skills.