linux-kernel - Re: [RFC PATCH 03/15] mm/vmalloc: introduce new vrealloc() call and its subsidiary reach analog

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Message-ID: <f9ee08f81b3c114b015643e1fca5b7a9@suse.de>
Date:   Thu, 10 Jan 2019 11:08:52 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Joe Perches <joe@...ches.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 03/15] mm/vmalloc: introduce new vrealloc() call and
 its subsidiary reach analog

On 2019-01-09 17:50, Matthew Wilcox wrote:
> On Wed, Jan 09, 2019 at 05:40:13PM +0100, Roman Penyaev wrote:
>> Basically vrealloc() repeats glibc realloc() with only one big 
>> difference:
>> old area is not freed, i.e. caller is responsible for calling vfree() 
>> in
>> case of successfull reallocation.
> 
> Ouch.  Don't call it the same thing when you're providing such 
> different
> semantics.  I agree with you that the new semantics are useful ones,
> I just want it called something else.  Maybe vcopy()?  vclone()?

vclone(). I like vclone().  But Linus does not like this reallocation
under the hood for epoll (where this vrealloc() should have been used),
so seems that won't be needed at all.

> 
>> + *	Do not forget to call vfree() passing old address.  But careful,
>> + *	calling vfree() from interrupt will cause vfree_deferred() call,
>> + *	which in its turn uses freed address as a temporal pointer for a
> 
> "temporary", not temporal.

Ha! Now I got the difference.  Thanks, Mathew :)

> 
>> + *	llist element, i.e. memory will be corrupted.

--
Roman