From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx160.postini.com [74.125.245.160]) by kanga.kvack.org (Postfix) with SMTP id 458846B00EA for ; Sun, 4 Mar 2012 12:51:36 -0500 (EST) Received: by pbbro12 with SMTP id ro12so4676043pbb.14 for ; Sun, 04 Mar 2012 09:51:35 -0800 (PST) Date: Sun, 4 Mar 2012 09:51:01 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH] mm: shmem: unlock valid page In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Hillf Danton Cc: Linux-MM , Andrew Morton , LKML On Sun, 4 Mar 2012, Hillf Danton wrote: > In shmem_read_mapping_page_gfp() page is unlocked if no error returned, > so the unlocked page has to valid. > > To guarantee that validity, when getting page, success result is feed > back to caller only when page is valid. > > Signed-off-by: Hillf Danton I don't understand your description, nor its relation to the patch. NAK to the patch: when no page has previously been allocated, the SGP_READ case avoids allocation and returns NULL - do_shmem_file_read then copies the ZERO_PAGE instead, avoiding lots of unnecessary memory allocation when reading a large sparse file. Hugh > --- > > --- a/mm/shmem.c Sun Mar 4 12:17:42 2012 > +++ b/mm/shmem.c Sun Mar 4 12:26:56 2012 > @@ -889,13 +889,13 @@ repeat: > goto failed; > } > > - if (page || (sgp == SGP_READ && !swap.val)) { > + if (page) { > /* > * Once we can get the page lock, it must be uptodate: > * if there were an error in reading back from swap, > * the page would not be inserted into the filecache. > */ > - BUG_ON(page && !PageUptodate(page)); > + BUG_ON(!PageUptodate(page)); > *pagep = page; > return 0; > } > -- > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org