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Message-ID: <4E3ADEFD.30501@linux.vnet.ibm.com> Date: Thu, 04 Aug 2011 11:03:41 -0700 From: Allison Henderson <achender@...ux.vnet.ibm.com> To: Mingming Cao <cmm@...ibm.com> CC: "Ted Ts'o" <tytso@....edu>, Ext4 Developers List <linux-ext4@...r.kernel.org> Subject: Re: [PATCH 1/1 v3] ext4: fix xfstests 75, 112, 127 punch hole failure On 08/04/2011 10:44 AM, Mingming Cao wrote: > On Thu, 2011-08-04 at 11:25 -0400, Ted Ts'o wrote: >> On Thu, Aug 04, 2011 at 12:22:58AM -0700, Allison Henderson wrote: >>> >>> Oh, I think we do avoid calling the unmap for this last condition >>> though. The first and last page offsets are calculated earlier for >>> calling truncate_inode_pages_range to release all the pages in the >>> hole. The idea is that everything from first_page_offset to >>> last_page_offset covers all the page aligned pages in the hole. So >>> then if offset and length are aligned, we basically end up with >>> first_page_offset = offset and last_page_offset = offset + length, >>> and the page_len will turn out to be zero. Right math? Maybe we >>> can add some comments or something to help clarify. >> >> Yeah, sorry, I wasn't clear enough about the condition. Consider the >> situation where we punch the region: >> >> 4092 -- 8197 >> >> In the previous section of code, we would zero out the byte ranges >> 4092--4095 and 8192--8197. What's left is a completely page-aligned >> range, which would have already been taken care of already. But since >> we're calculating based on offsets, I believe there will be an >> unnecessary call to ext4_unmap_page_range(). >> > > Yep, for the default 4k block size, if the offset is not block aligned, > with the patch we could end of unnecessary unamp_page_range. > >> BTW, the name ext4_unmap_page_range() is a bit confusing; maybe we >> should rename it to ext4_unmap_partial_page_buffers()? >> > > The new name sounds better. It should only called for punch hole in the > range (blocksize != pagesize) and (offset is block aligned) and (offset > is not page aligned) > >> I know you were copying from the ext4_block_zero_page_range() function >> and its calling sequence (but in my opinion that function wasn't named >> well and the comments in that code aren't good either). >> >> I also wonder why we can't fold the functionality found in >> ext4_unmap_page_range() into ext4_block_zero_page_range(). Did you >> look into that option? >> > > ext4_block_zero_page_range() also called from ext4 truncate code path, > which only zero out within a block, but do not need to handle the > partial page unmap. There are two logical steps need by punch hole, one > is to zero out the non-block-aligned portion(like truncate), second is > to unmap_partial_page_buffers(). It seems cleaner to separate the two > logical steps out from the code simplify point of view. > > Regards, > Mingming Yeah looking at them again, I think I like the simpler v3. V2 does both operations in one loop, but I think it's cleaner to keep them separate. Allison Henderson >> Regards, >> >> - Ted >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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