linux-kernel - Re: [PATCH 01/12] uprobes: split THPs before trying replace them

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Message-Id: <20170126025408.GB11569@linux.vnet.ibm.com>
Date:   Wed, 25 Jan 2017 18:54:08 -0800
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 01/12] uprobes: split THPs before trying replace them

> > 
> > The first time the breakpoint is hit on a page, it replaces the text
> > page with anon page.  Now lets assume we insert breakpoints in all the
> > pages in a range. Here each page is individually replaced by a non THP
> > anonpage. (since we dont have bulk breakpoint insertion support,
> > breakpoint insertion happens one at a time). Now the only interesting
> > case may be when each of these replaced pages happen to be physically
> > contiguous so that THP kicks in to replace all of these pages with one
> > THP page. Can happen in practice?
> > 
> > Are there any other cases that I have missed?
> 
> We use a hack in our applications where we open /proc/self/maps, copy
> text segments to a staging area, then create overlay anon mappings on
> top and copy the text back into them. Now we have THP-backed text and
> very little iTLB pressure :-)
> 
> That said, we haven't run into the uprobes issue yet.
> 

Thanks Johannes, Kirill, Rik.


Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>