linux-kernel - Re: [PATCH v3 2/2] mm: rid swapoff of quadratic complexity

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Message-ID: <CANaguZDcJa9NxZU4Z3Q7DqvQK5zsDXZKNbhbO8fcppnYrTxMHw@mail.gmail.com>
Date:   Wed, 2 Jan 2019 15:05:25 -0500
From:   Vineeth Pillai <vpillai@...italocean.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Kelley Nielsen <kelleynnn@...il.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v3 2/2] mm: rid swapoff of quadratic complexity

On Wed, Jan 2, 2019 at 2:43 PM Hugh Dickins <hughd@...gle.com> wrote:

>
> Wrong.  Without heavier locking that would add unwelcome overhead to
> common paths, we shall "always" need the retry logic.  It does not
> come into play very often, but here are two examples of why it's
> needed (if I thought longer, I might find more).  And in practice,
> yes, I sometimes saw 1 retry needed.
>
Understood. Sorry, I missed these corner cases.

> I don't use frontswap myself, and haven't paid any attention to the
> frontswap partial swapoff case (though notice now that shmem_unuse()
> lacks the plumbing needed for it - that needs fixing); but doubt it
> would be a good idea to refactor it out as a separate case.
>
I shall rework the shmem side to take care of the frontswap and retain
the retry logic in a simplified manner.

Thanks again for all the comments and insights..

~Vineeth