linux-kernel - Re: [PATCH] mm/gup.c: Handle error at earliest for incorrect nr

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Message-Id: <20200430142311.091b82235141ca47b9c6475a@linux-foundation.org>
Date:   Thu, 30 Apr 2020 14:23:11 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/gup.c: Handle error at earliest for incorrect
 nr_pages value

On Fri,  1 May 2020 01:41:58 +0530 Souptick Joarder <jrdr.linux@...il.com> wrote:

> As per documentation, pin_user_pages_fast() & get_user_pages_fast()
> will return 0, if nr_pages <= 0. But this can be figure out only after
> going inside the internal_get_user_pages_fast().
> 
> This can be handled early. Adding a check for the same.

Calling get_user_pages() for (nrpages <= 0) is a nonsensical thing to
do so it isn't a thing we should care to optimize.  Adding new checks
will actually slow down the use cases which we *do* care about.  And it
adds more code.